Hello Djan
These acronyms display several attributes of the IPv6 address, and are always displayed after the address itself. These are part of the output of the show ipv6 interface command. Specifically, the [EUI/CAL/PRE] acronyms you mention are indicating that:
EUI - Extended Unique Identifier. The address was generated using EUI-64, a method by which the IPv6 address is derived from the MAC address of the interface.
CAL - Calendar. This means that the address is timed and has valid and preferred lifetimes.
PRE - Preferred. This timed address is preferred.
There are several other attributes as well and you can find them at this Cisco Command Reference link for the show ipv6 interface command.
I hope this has been helpful!
Laz