To smooth out a jagged or stair-step appearance or motion between adjacent points so that it appears continuous.
If you have played game in low/medium setting. Anti alising is a technique used to smooth otherwise jagged lines or textures by blending the color of an edge with the color of pixels around it.
There are different kinds of anti-aliasing, and some are more performance-intensive than others.
For example, FXAA stands for "Fast Approximate Anti-Aliasing" and does not require a large amount of computing power. It achieves this by smoothing out jagged edges based on how they appear on the screen in pixels, rather than analyzing the 3D model itself, as with traditional anti-aliasing.
Another type is SSAA (Super-Sampling Anti-Aliasing) which is very performance intensive. In SSAA, multiple locations are sampled within each pixel, and each of these samples is fully rendered and combined with the others to produce the final displayed pixel.
MSAA (Multi-Sample Anti-Aliasing) is somewhere in the middle. It isn’t as performance-intensive as SSAA, but more intensive than FXAA.