Dera is a Punjabi word of Persian origin meaning camp, abode, tent, house, temple, sacred shrine or habitation. In Sikh literature it has been used for camp and cantonment (1). Some Gurdwaras have been called as dera - e.g : Gurudwara Dera Sahib, Dera Baba Nanak, Dera Baba Beeram Shah, etc. In SGGS word Dera it has been used for abode (p.256) ਡੇਰਾ ਨਿਹਚਲ ਸਚ ਸਾਧਸੰਗ ਪਾਇਆ ॥ That permanent and true place is obtained in the Saadh Sangat, the Company of the Holy; as well as cantonment (p.628) (I was NOT ABLE TO FIND in the SGGS website link, so please find the right page).
Reference: 1. The encyclopedia of Sikhism: By H. S Singha