If a spell fails, do you lose the spell completely, or just A spell?

[Where is my drink]

Most things basically say "if you fail you lose the spell" or something to that accord.

Im wondering if i have-say 3 level 3 spells, and i use one and it fails, or someone counters it or whatever.. Do i lose that spell, even though i could cast 2 more of the same spell because i have 2 level 3s left, or is that spell out of my list for the day, regardless of whether or not i have 2 "more" of it.

Is it just that spell on its own and its own casting that fails. Or do i lose that actual spell completely off the list?

Sorry if this is confusing, im just curious.

Spontaneous or prepared, how does this work?

[ShadowcatX]

It is just that specific casting of the spell.

[Hendelbolaf]

If you are a spontaneous caster, you lose a slot for the day.

If you are a prepared spellcaster, you lose the spell that you tried to cast.

[Ximen Bao]

I think you wanted to loose it but instead you lose it.

[YogoZuno]

To answer the original question a little clearer, as a prepared caster, if a spell fails, then you only lose the specific instance of that spell you were trying to cast. If, for instance, you have 3 magic missiles memorised, and you fail a concentration check while casting the first, you still have 2 available. In the same way, if you had 2 normal magic missiles memorised, and an empowered magic missile, and you failed to cast a normal magic missile, you would still have a normal and an empowered magic missile memorised.

For spontaneous casters, it is essentially the same, but replace 'memorised spell' with 'spell slot'.