In grammar, the term weak (originally coined in German: schwach) is used in opposition to the term strong (stark) to designate a conjugation or declension when a language has two parallel systems.
This differs from the situation in nouns and verbs in that every adjective can be declined using either the strong or the weak declension.
Examples: In other languages the strong-weak polarity is used to express distinctions that may or may not be analogous.
These can be strong (able to carry a full syllable) or weak (likely to collapse under the weight of a prefix or suffix).
The terms "weak" and "strong" rarely overlap with the idea of "regular" and "irregular"; some descriptions of English verbs contrast "weak" with "irregular", but this is misleading.