FIR filter
A digital filter that only looks at incoming samples, never at its own output — so it is always stable and can be made perfectly phase-linear.
Each output sample is a weighted sum of the last N input samples. The weights are called taps, and they are also the filter's impulse response, which ends after N samples — hence finite. No feedback means the filter cannot oscillate, and with symmetric taps every frequency is delayed by exactly the same amount.
That is the basis of linear-phase EQ in mastering, where the phase shift of an ordinary filter would be unwelcome. The cost is latency and CPU: a steep low-end cut can need thousands of taps, and the DAW has to hide the delay with plugin delay compensation. Linear phase also brings its own artefact, pre-ringing, a faint smear that arrives before the transient does. A convolution reverb is, underneath, one enormous FIR filter.