The anapest builds momentum by delaying the beat: two quick light syllables, then the strike. That delay-and-release gives anapestic verse its rolling, comic, or cavalry-charge energy - Byron's Sennacherib, Clement Moore's 'A Visit from St. Nicholas', and Dr. Seuss all ride it.
Four anapests make anapestic tetrameter; three make trimeter. Limericks mix anapestic trimeter (lines 1, 2, 5) with anapestic dimeter feel (lines 3, 4) over an AABBA rhyme scheme - which is why our Limerick Checker listens for both the rhyme pattern and the anapestic bounce.
In strict prosody the anapest also appears as a substitution inside iambic lines, where two iambs compress into one anapest. Classical quantitative verse has a different creature with the same name (two short syllables plus a long); the Latin and Greek tools handle that system separately.
Test anapestic bounce with the Limerick Checker for comic forms or the Poetry Meter Checker for narrative verse like Byron's.