802 is an IEEE(Institute of Electrical and Electronics Engineers) project which standardizes  LAN (Local Area Networks)  and MAN (Metropolitan Area Networks) communication protocols and it gives a number after 802 and a dot for a specific Network, such as, Ethernet  standardized  as  802.3 and WiFi  as 802.11 which are popular standards for wired LAN and wireless LAN respectively. Further, actually Ieee 802 project specifies the physical and the data link Layer model in TCP/IP stack  which is  jointly network access layer in TCP/IP model. The reason behind to need a specification for physical and the link layer can be understood by  different between  Ethernet  (IEEE 802.3)  and  WiFi (IEEE 802.11) local area networks  .

Original TCP/IP Stack

Moreover, when communication medium changes form wired to wireless the physical layer and data link layer need to be redesigned, for example in 802.3 at the  data link layer there is no need of acknowledgement because  on wired link there is probability of packet error is almost negligible but in 802.11 there is need of acknowledgement packet  because probability of packet error on the wireless link is very high.
                                                     

Modified TCP/IP Stack

Another example is that Zigbee  ( IEEE 802.15.4 specification) which is used by sensor network in which the data rate needs  very low  which is 200 kbps to 300 kbps because high data rate consumes high energy  so 802.11 specification will not be useful for sensor networks.