Crystals are sometimes used in a circuit which has an output close to an integral multiple of the crystal frequency. This circuit is called:

A circuit designed to excite a crystal so that it resonates at a multiple of its fundamental frequency is called an overtone oscillator. Crystals naturally possess mechanical resonances at odd harmonic multiples (such as the 3rd, 5th, or 7th) of their fundamental frequency. Operating a crystal at one of these higher mechanical resonances directly is different from using a standard 'frequency multiplier', which takes a fundamental electrical signal and distorts it to extract harmonics. Distractors like 'crystal ladder' and 'crystal lattice' refer to types of RF filters made by wiring multiple crystals together, not to oscillator circuits.