In SNMP protocol version 1 and 2c, a "community" denotes a group comprising one or more management platforms and several SNMP agents handled by these platforms.
Every community is identified by a community string. The community string is a nonencrypted component of every SNMP request and identifies the sender of the request as a member of the community concerned. Authorization for a read or write request which a management platform sends to an SNMP agent is controlled with this community string.
The community string makes a simple authentication mechanism available in SNMP. Management platforms and SNMP agents may only communicate with one another if they belong to the same community: the SNMP agent will only accept SNMP requests from management platforms whose community strings are known to it, i.e. preconfigured.
Since the community string is sent in non-encrypted form with the SNMP message, it is always at a risk of being used without authorization. This can be problematic for using SNMP with security in mind. On the other hand, most communities use the preset community string "public" in any case.
Select suitable communities corresponding to the organization of your systems and operations and assign suitable community strings to them. Change the community string in accordance with the guidelines of your manual: in a similar way, for instance, as for passwords. Note that you must modify the community string in all participating systems in the community.
If the environment of your SNMP agents and management platform(s) allows you to do so, use the user-specific authentication available with the SNMPv3 protocol.