Sampling

EEVEE uses a process called Temporal Anti-Aliasing (TAA) which reduces Aliasing. TAA is sample based so the more samples the more aliasing is reduced at the cost of performance.

Reference

Panel:

Render ‣ Sampling

Viewport

The number of samples to use in the 3D Viewport. When setting this to zero the viewport will be resampled continuously.

Render

The number of samples to use in the final render.

Viewport Denoising

Reduces noise while moving the viewport or during animation playback.