https://en.wikipedia.org/wiki/Passerine
Passerine is the largest order of birds with more than 6,500 species, including songbirds, wrens, and crows. They have anisodactyl toes, diverse vocalizations, and altricial chicks.

https://www.britannica.com/animal/passeriform
Passeriform, also known as passerine or perching bird, is the largest order of birds with about 5,700 species. It includes songbirds, finches, shrikes, and many other groups with diverse feeding adaptations and colorful plumage.

https://simple.wikipedia.org/wiki/Passerine
Passerine is a term for small or medium sized birds of the order Passeriformes, which includes more than half of all bird species. Learn about their adaptations, evolution, taxonomy and diversity, with examples and images.

https://www.worldatlas.com/articles/what-are-passerine-birds.html
Passerine birds are the largest order of birds, with more than 6,000 species and diverse features. They have specialized feet for perching, vocal organs for singing, and are found in all continents except Antarctica.

https://www.merriam-webster.com/dictionary/passerine
Passerine is an adjective or noun that refers to the largest order of birds, mostly songbirds with perching habits. Learn the etymology, examples, and word history of passerine from Merriam-Webster dictionary.

https://www.newworldencyclopedia.org/entry/Passerine
Passerine is a term for perching birds or songbirds, the largest order of birds with over 5,400 species. Learn about their characteristics, suborders, evolution, and fossil record from this online encyclopedia article.

https://www.mdahlem.net/birds/passer.php
The answer is quite straight-forward, once one knows the Latin name of the common House Sparrow - "Passer domesticus". Passerines are birds that, like the House Sparrow, have three toes forward, one backward, e.g. when sitting on a perch, non-passerines don't. As a rule of thumb, songbirds are passerines, others are not.

https://www.britannica.com/animal/passeriform/Form-and-function
Passerines are birds with diverse feet, bills, and adaptations for perching, walking, running, swimming, and feeding. Learn about the features, types, and functions of passerine feet, bills, and tarsi from Britannica.

https://www.britannica.com/animal/songbird
Songbird is a term for any member of the suborder Passeri, which includes about 4,000 species of birds in 35 to 55 families. Songbirds are known for their vocal organ, or syrinx, and their varied songs, which are used for courtship, breeding and communication.

https://www.allaboutwildlife.com/passerines/
A passerines is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it is roughly twice as species rich as the largest of the mammal

https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/perching-birds-passeriformes
Learn about the order of passerines, also known as perching birds or songbirds, which includes over half of all bird species. Find out their physical characteristics, geographic range, habitat, diet, behavior, and reproduction.

https://animalia.bio/passeriformes
Passeriformes, also known as passerines, perching birds, or songbirds, are the largest and most diverse order of birds. They have three forward-pointing toes and include sparrows, finches, cuckoos, shrikes, and many other families.

https://web.stanford.edu/group/stanfordbirds/text/essays/Passerines_and_Songbirds.html
Learn about passerines, the perching birds that make up 60 percent of all bird species. Find out how they are classified, what makes them successful, and how they differ from nonpasserines and suboscines.

http://tolweb.org/passeriformes
The Passeriformes (or 'passerine' birds) are synonymous with what are commonly known as "perching birds"; this group also contains within it a major radiation commonly known as songbirds (oscine Passerines or Passeri). Of the 10,000 or so extant species of birds, over half (~5,300) are perching birds.

https://www.cell.com/current-biology/fulltext/S0960-9822(22)01383-5
Passeriformes, more commonly known as perching birds or passerines, are the most species-rich group of birds. Totaling nearly 6500 species, approximately two out of every three bird species is a passerine. Passerines are globally distributed and are among the most abundant birds at nearly every terrestrial location on Earth.

https://www.sciencedirect.com/science/article/pii/S0960982222013835
Passeriformes, more commonly known as perching birds or passerines, are the most species-rich group of birds. Totaling nearly 6500 species, approximately two out of every three bird species is a passerine. Passerines are globally distributed and are among the most abundant birds at nearly every terrestrial location on Earth.

https://en.wikipedia.org/wiki/Songbird
Songbirds are birds that belong to the suborder Passeri of the perching birds (Passeriformes), which have a diverse and elaborate vocal organ and song. Learn about their origin, distribution, diversity, and how they use song for communication, courtship and sexual selection.

https://www.britannica.com/animal/passeriform/Ecological-importance
Passerines are the dominant form of birdlife in virtually all terrestrial environments and have diverse breeding behaviours, nests, and diets. They also play a major role in pollination, seed dispersal, and food chains, and some are brood parasites or have elaborate displays.

https://link.springer.com/referenceworkentry/10.1007/978-3-319-47829-6_907-1
Learn about the reproduction, growth, and survival patterns of passerines, the most diverse and species-rich order of birds. Explore how passerines exhibit behavioral plasticity, learning, and intelligence in various mating systems and social contexts.

https://lafeber.com/vet/passerine-anatomy-ten-key-facts/
Learn about the diversity, structure, and function of passerine birds, also known as perching birds or songbirds. Find out how passerines use carotenoids, testosterone, and song to communicate and reproduce.

https://academic.oup.com/bioscience/article/50/6/487/261005
Learn about the diversity, history, and adaptations of passerines, the largest group of birds with nearly 60% of extant species. Explore how phylogenetic methods based on anatomy, molecular, and behavioral characters have revealed the monophyly and evolution of passerines.

https://www.britannica.com/animal/passeriform/Classification
Passeriform - Songbirds, Perching, Taxonomy: Passerine birds are distinguished by a suite of unique derived characters, including the aegithognathous structure of the palate, syringeal anatomy, multiple characters of the anisodactyl foot, insertion of the forearm muscle tensor propatagialis brevis, and spermatozoa with a coiled head.

https://www.britannica.com/animal/passeriform/Skeleton
Skeleton. Of the many variations in passerine skeletal structure, only a few that are important in classification are mentioned here.. In the skull the bony palate, composed of a number of small bones, is termed aegithognathous; also found in swifts (Apodidae), this palatal type is characterized by the shape and type of fusion of the small bones of the palate.