Sticks and stones may indeed break bones, but your spells and abilities can't target me or mine.
(In truth and in short, it's a keyword ability that precludes a permanent or player from being targeted by an opponent.)
"You can't hit a target you cannot see,
and you cannot see a target you do not have."
-- Zig Ziglar
In Magic: The Gathering, as covered by CR 702.11. and subsections, hexproof is an evergreen static ability of a permanent that was officially keyworded in 2012 and means said permanent cannot be the target of spells or abilities one's opponent(s) control. Likewise, on a player it's officialese is “You can’t be the target of spells or abilities your opponents control.” Multiple instances of the same hexproof ability on the same permanent or player are uselessly redundant, providing no additional benefits.
Hexproof from (quality) is a variant of hexproof that, when on a permanent, means said object cannot be the target of (quality) spells one's opponent(s) control or abilities the opponent(s) control from (quality) sources.” Qualities in use as of September 2024 include: planeswalkers; monocolored; multicolored; white; blue; black; artifacts, creatures, and enchantments; and activated and triggered abilities.
Hexproof from blue (quality A) and from black (quality B) is shorthand for “hexproof from quality A (blue)” and “hexproof from quality B (black)”; it behaves as two separate hexproof abilities. Hexproof from each color (characteristic) is shorthand for “hexproof from quality A (white),” “hexproof from quality B (blue),” and so on for each possible quality the listed characteristic could have, which in this example is five (white, blue, black, red, and green); it behaves as multiple separate hexproof abilities. Thanks to Veil of Summer and Breaker of Creation for providing examples.
A hexproof counter on a permanent or on a card in a zone other than the battlefield causes that object to gain and have hexproof, and that effect is applied in layer 6, just like other ability-adding and ability-removing effects as well as effects that say an object can't have an ability.
Any effect that causes an object (permanent or player) to lose hexproof will cause an object to lose all hexproof from (quality) abilities. Any effect that allows a player to choose a creature with hexproof as a target as though it didn’t have hexproof will allow a player to choose a creature with a hexproof from (quality) ability. Any effect that looks for a card with hexproof will find a card with a hexproof from (quality) ability. Hexproof from is a hexproof ability.
Well-known cards affecting hexproof, at least in the Commander community, are Swiftfoot Boots and Archetype of Endurance. There are more, of course, and sure to be more in the future.
In real life, and some works of fantasy, hex-proof results from certain types of defensive counter-magic.
Source:
https://magic.wizards.com/en/rules