Meaning of SDS rotary hammer specifications?

In the description of an SDS rotary hammer such as "Makita HR3210C 1-1/4-Inch SDS-PLUS", what does the "1-1/4 inch" refer to?

For an ordinary drill, the "1-1/4 inch" would be the max diameter bit than can be chucked. But "SDS-PLUS" is a special type of chuck that is not turned to adjust its diameter. Do SDS-PLUS bits have various size shanks? Does the "1-1/4 inch" refer to the largest size shank that will fit the hammer?