What does isosceles mean in geometry?

Hint: We first define the term isosceles for the geometry. Then we take the general figure which is used to describe the term isosceles for triangles. We use the figure to explain the concept and explain different parts of the triangle.

Complete answer:
In general, isosceles means two sides being equal. The most commonly used diagram for the term isosceles is triangle. The isosceles triangle is the triangle which has two of its consecutive sides being equal in length.

In the above image $\Delta ABC$ is an isosceles triangle. The properties for isosceles triangle are that the opposite angles of the equal sides are also equal.
Therefore, for $\Delta ABC$, we have $CA=CB$ and also $\angle CAB=\angle CBA$.
Most of the time, the unequal side of the triangle is considered as the base.
The altitude of an isosceles triangle is measured from the base to the vertex(topmost) of the triangle.
Based on the angle value, the isosceles triangle can be broken into many parts like isosceles acute, isosceles obtuse, and isosceles right-angle triangles.

Note:
The altitude of the triangle forms the required right angle and the altitude becomes the
shared legs. Also, the congruent legs of a triangle become the congruent hypotenuse. Therefore, the
altitude drawn to the base of the isosceles triangle bisects the base.