Overlapping triangles are those that touch or almost touch each other, no matter what angle or orientation they have. The Overlapping triangles detection function is available in the context menu after a right-click on the screen.
In the dialogue, you can determine the max. distance of parts. All triangles below that value will be selected. Same with the max. angle. Below you can set the direction of the triangles. With Parallel, all triangles that have the same orientation, will be selected. With Antiparallel, it’ll be all triangles with an opposite direction. Or you can also select in both directions. If you want to fix your parameters as standardized settings, press Save settings as default. If you want to get back to previous values after you’ve changed them, click on Restore settings.