1. In zoology, a winglike projection or structure: The sphenoid bone, or ala, is one of seven bones which is somewhat shaped like the wing extension of a bat.
2. A flat process or part of an organism that is shaped like a wing: An ala is the lateral petal of a papilionaceous flowers.

An ala is also the membranous expansion on some seeds.

The basal lobe of moss leaves is called an ala.