The phrase "vibration feature" refers to a function or capability of a device that enables it to produce a shaking or vibrating sensation. Full definition
It's very easy to rock this sleeper and when you stop rocking to sleep baby the calming vibrations features help to soothe and relax. (momsandbabyzone.com)
It also has a soothing vibration feature with two speeds, which works whether it's in swing or rocker mode. (checkpregnancy.com)
It has a soothing vibration feature that many parents actually used at baby's bedtime, with surprisingly good results! (newmomstuff.com)