Each tap in an FIR filter represents one sample of delay in the filter's impulse response. A 1,024-tap filter at 48 kHz represents 21ms of filter length. More taps allow: steeper filter slopes, finer low-frequency resolution, and more precise correction of room modes.
The trade-off: longer filters add latency and use more processing power. A 65,536-tap filter for precise sub-bass correction adds 682ms latency — fine for playback/mixing, unusable for live monitoring. Most room correction systems use shorter filters for real-time use and offer longer filters for mixing/mastering.