Bet Selection: a way to choose betting locations (in any form or shape). A bet selection is a flat bet.

Money Management: is any progressive scheme, defined as not being flat betting. Both positive (up as you win) as well as negative (up as you lose).

System/Method: Is a combination of Bet Selection and Money Management with a win goal, as well as a stop-loss per session.

Strategy: Is a broader concept which implicates elements such as using systems, inter-session money management, recovery modes, unit value modification, lifetime bankroll management and in general a plan for using systems, bet selection and money management schemes as a whole intended to having a shot at winning.