There is a standard for all WiFi devices (router and access points). The publisher of this standard is the Institute of Electrical and Electronics Engineers (IEEE). All standards related to wireless networks are summarized under IEEE 802.11.
Today, IEEE 802.11n or IEEE 802.11ac are the common standard. These are constantly being developed and are usually downward compatible.
Generally speaking, the standard determines how much data throughput, expressed in megabits per second (Mb/s) or megabytes per second (MB/s), is offered by the WiFi.