Secon language acquisition is the process by which people learn a second language in addition to their native language(s). The term second language is used to describe the acquisition of any language after the acquisition of the mother tongue. There is also research into the similarities and differences of Third Language Acquisition. The language to be learned is often referred to as the "target language" or "L2", compared to the first language, "L1". Second language acquisition may be abbreviated "SLA", or L2A, for "L2 acquisition".