Of course, the tangent is not the only useful ratio. Other ratios have been defined
too. So here are some more definitions :

In a right triangle the sine (or sin for short) of an acute angle is defined
as the ratio between the side opposite it and
the hypotenuse.

Look at the figure on the right where sin(A)=BC/AC.

The cosine (or cos for short) of an angle is defined as the ratio between the leg
right next to the angle and the hypotenuse.

In the triangle on the right you see cos(A)=AB/AC.

The last one is the cotangent (or cot for short). It is defined as the ratio between the
leg right next to the angle and
the leg opposite of the angle.

So you have cot(A)=AB/BC.

Note that the cotangent is the inverse
of the tangent. That means that if the tangent of an angle has a value of 1/2, then the cotangent has a value of 2/1.