A line of very popular Android smartphones from Samsung, starting with the Galaxy A3 in 2014.  The Galaxy A series is priced lower than Samsung's flagship Galaxy S series.  However, the CPUs in the A models are a bit slower, and there is less storage and RAM than their S counterparts.  However, Galaxy A prices can be half or less than the S models.  See 
Galaxy S, 
Galaxy C and 
Galaxy Fold.