weak

Weak is an adjective used to describe a lack of strength, power, or effectiveness. It can apply to physical objects (a weak rope), living beings (a weak immune response), signals (a weak transmission), or efforts (a weak excuse). The noun form is weakness, and the adverb is weakly. The term appears across everyday language as well as in science and technology.

In physics, the weak interaction is one of the four fundamental forces, together with gravity, electromagnetism, and the strong nuclear force. It governs certain forms of radioactive decay, such as beta decay, and neutrino interactions. It is mediated by the W and Z bosons, operates over a very short range, and is weaker than the strong force. It also violates parity, and in some processes, charge-parity symmetry. The electroweak theory unifies the weak and electromagnetic forces.

In mathematics, “weak” describes alternative notions of convergence and topology. Weak convergence of a sequence in a normed space means the sequence converges when tested against all continuous linear functionals, a weaker condition than convergence in norm. The weak topology on a space is the coarsest topology that makes all continuous linear functionals continuous; these ideas are central to functional analysis and optimization.

In computing and artificial intelligence, “weak” appears in phrases such as weak AI, referring to systems designed to perform specific tasks rather than general intelligence. The term also appears in programming to describe weak typing, where a language allows implicit type coercions, reducing strict type safety.