Subtype of the instrument synthesizer: https://musicbrainz.org/instrument/4a29230c-5ab5-4eff-ac59-4a253f3561a0

A "sampler" is a specific type of synthesizer where the sound generator consists of (usually short) recorded sounds.

The most common type of sampler is the "digital sample-based subtractive synthesizer". This is essentially a subtractive synthesizer. (What is "subtractive synthesis: most analog synthesizers we know are subtractive synthesizers, but also digital synths use this model. What defines this type of sound synthesis, is a sound generator provides a sound rich in harmonics, which is then modified by filtering out harmonics, other standard components are LFO and envelope generators to modulate various parameters).

Most samplers have LFO's and envelope generators.

Some samplers are able to stack up sounds, introducing an additive component (additive synthesis is basically starting from pure sounds, poor in harmonics, and stacking them up to create a "rich" sound, such as FM synthesis or organs.)

A sampler should not be confused with a recording device, which is a piece of gear designed to record sound with the intention to playback the sound as accurate as possible. A sampler is specifically designed as an instrument, where a recording is used as a base component to create new sounds, or music. Either melodically, or rhythmically.

The simplest sampler consists of a small memory to record sounds, as record button, and a trigger button. This trigger button is then used to create a rhythmic pattern with the recorded sound. It is comparable to an analog synth with only a VCO (oscillator) and a single trigger button.

Some samplers are complex synthesizers.

Samplers are related to "romplers", with the difference the rompler is bound to built in sounds (often with expansion cards), while the sampler allows for the creation of a custom wavetable as sound source for the synthesizer design.

A archetypical example of a sampler is the Akai S1000: https://en.wikipedia.org/wiki/Akai_S1000