IEEE 802.11s is a draft IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad-hoc networks.
802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a, 802.11b, 802.11g, and 802.11n versions to provide wireless connectivity in the home, office and some commercial establishments.
Meanwhile, open80211s is a consortium of companies who are sponsoring (and collaborating in) the creation of an open-source implementation of the emerging IEEE 802.11s wireless mesh standard. The resulting software will run on Linux on commodity PC hardware.