One triangle is isometric to another triangle if it has the same size and shape. This means that it must have the same angles and side lengths as the other triangle.
Applying an isometric transformation to a triangle produces a new triangle that is isometric to the first. The isometric transformations are translation, which moves the triangle to a new position in the graph, reflection, which flips the triangle across a line, and rotation, which turns the triangle around the origin of the graph. A triangle that is produced by one of these transformations retains the size and shape of the original.