what is sin and cos

Sin and Cos are two trigonometric functions.
Suppose we have an angle $\theta$ as shown below in right triangle ABC;

Here we have;
$$\begin{gathered} \mathrm{Sin\theta } = \frac{\mathrm{Perpendicular}}{\mathrm{hypotenuse}} = \frac{\mathrm{AB}}{\mathrm{AC}} \\ \mathrm{And}, \mathrm{Cos\theta } = \frac{\mathrm{Base}}{\mathrm{Hypotenuse}} = \frac{\mathrm{BC}}{\mathrm{AC}} \end{gathered}$$
And relationship between $\mathrm{Sin\theta } \mathrm{and} \mathrm{Cos\theta }$ is given by;
${\mathrm{Sin}}^2\mathrm{\theta }+{\mathrm{Cos}}^2\mathrm{\theta } = 1$