Beer comparison
Pilsner vs lager: one is a style, the other is the family.
Every pilsner is a lager. Not every lager is a pilsner. That one sentence clears up most of the confusion.
Where pilsner fits
Pilsner is the pale, crisp branch that became famous worldwide.
The original Pilsner was brewed in Plzeň in 1842. Its pale colour, clear appearance, firm hop bitterness and cool lager fermentation created a style that was widely copied.
But lager itself is much older and much broader. Helles, dunkel, bock and schwarzbier all belong to the lager family even though they can look and taste very different from pilsner.
Side by side
A useful shopping clue
If a label says “lager”, ask what kind.
“Lager” by itself tells you about fermentation family, not the whole flavour. “Pilsner” narrows the expectation towards pale colour, crispness and more obvious hop bitterness. Helles points you towards softer malt; dunkel towards darker malt; bock towards more strength and richness.
Ale vs lager