The phrase "fluid movement" means moving smoothly and gracefully, without any stiffness or jerky motions. It implies a natural and effortless way of moving. Full definition
The bosses seem lively with fluid movement, and the backgrounds can sometimes play into how a fight is handled, or sometimes have their own element of animation. (thatvideogameblog.com)
It keeps them comfortable, helps them to get up easier, improves their flexibility and give them more fluid movement. (naturalstride.com)
There is also a slide and wall run mechanic that when all combined, create an incredibly fluid movement system that really helps make the player feel like a super ninja. (thevrgrid.com)