"tan" means the tangent function of one of the acute angles.
It's the ratio of the length of the opposite side to the length of the adjacent side.
If you say that tan(a) = 3/4, then in the same triangle, the hypotenuse is 5 , and
now that we know all the sides, we can state all the other trig functions of that angle.
opposite = 3
adjacent = 4
hypotenuse = 5
sin(a) = opp/hyp = 3/5
csc(a) = hyp/opp = 5/3
cos(a) = adj/hyp = 4/5
sec(a) = hyp/adj = 5/4
tan(a) = opp/adj = 3/4
cot(a) = adj/opp = 4/3