AC means Alternating Current, electrical current that periodically reverses direction, and DC means Direct Current, a current that continuously flows in one direction. AC/DC on a socket means it can take both types of power.

I’ve seen an incredible number of people who were never taught to properly touchtype and where each finger goes and developed bizarre techniques to type with 4, 6, or 8 fingers that may be almost as fast as the proper one but horrendously non-ergonomic. Ubiquity of staggered layouts (instead of proper ortholinear) does not help — it’s almost like it’s begging to type Z with ring finger and X with middle one.