How the terms are built
Combined, every surface but the last drops its -al for -o: mesial + occlusal + distal → mesio-occluso-distal.
Order: mesial or distal first, then the facial or oral face, occlusal or incisal last. Restorations keep one exception: MOD.
Same face, different word: labial on front teeth, buccal on back teeth; palatal on the upper arch, lingual on the lower.