In addition to what Balaji has already noted, I believe (?) the "6" means its a Catalyst 6000/6500 line card, the "1" basically a particular line card variant, the "48" the number of ports on the card, and the "a" an later/improved version of the line card.
For the Catalyst 6Ks, this might help you:
https://www.cisco.com/c/en/us/products/switches/catalyst-6500-series-switches/relevant-interfaces-and-modules.html
