An anapestic foot (known as an anapest) has two short syllables followed by a long syllable (SSL, or UU/).
Hexameter is six feet per line.
Again, this seems far from being a popular combination of foot and metre, but poets sometimes include a line of anapests among other rhythms, as in the example below. The fourth line is perfect anapestic hexameter:
Fled foam underneath us and 'round us, a wandering and milky smoke
As high as the saddle-girth, covering away from our glances the tide;
And those that fled, and that followed, from the foam-pale distance broke;
The immortal desire of immortals we saw in their faces, and sighed.
W.B. Yeats – from The Wanderings of Oisin
A closer look at the feet in this line
U = short syllable; / = long syllable; | = division between feet