explain to me the mathematics of a blocking bet

[ipokeder]

the use of "fake blocking bets" is very common in mid-high stakes as bluff-inducing bets, but personally i never use any actual blocking bets in my game and to an extent i feel like i'm not really sure what they are or what purpose they should serve. and since i don't use any real blocking bets, i don't think it makes sense for me to incorporate fake blocking bets against competent opponents, so i'd like for someone to explain to me the mathematics in which a blocking bet (excluding metagame considerations that i can make fake blockers in the future and whatnot) is the most +EV play

assuming the villian is rational and good

say for example, i have 44 w/ 4d on a 3c 6d 7d 8d 2d board and i block-bet the river

or i have JJ in an RR'd pot, the board is Qs Tc 5s 4c Th and i block-bet the river

are these examples of blocking bets? is a blocking bet fundamentally different from a bet/folding hand (because i always consider that a value bet, even if i'm thinly vbing an underpair or something but definitely folding to a raise)

i've always had the intuitive feeling that if i think i'm ahead in a hand i should be check/calling or value betting to get calls from worse hands or if i feel i'm behind i should be check/folding or bluffing to make him fold his hand, but i don't understand where block-betting comes into this (assuming block-betting is not simply bet/folding)

thanks