Definition
Binary features is a proposed system used refer to distinctive features which can be described in terms of positive value [+], indicating the presence of a feature, or a negative value [-], indicative of a phoneme lacking a certain feature (Zsiga, 2013).
Describing sounds in terms of binary features allows linguists to describe sounds in a more refined manner, as there may be variation in sounds across speakers within in a language, or across languages.
Features that are described as having binary [+/-] values include:
INLP Linguistic Glossary 