What is 'one turn' in Bravely Default?

Question

I know the how Brave and Default work. But something I have not quite paid attention to is what spells like Free Lunch that 'Make MP cost 0 for "two turns"' ACTUALLY mean.

If I Brave 3 times (so when I am up, I do 4 attacks) is that "four turns" so my fourth attack will cost normal MP?

Turn 1: (Free Lunch, Free Summon, Free Summon, 40 MP Summon)

Or is that "one turn" and the next time I get to go I have four more free spells again?

Turn 1: (Free Lunch, Free Summon x3) Turn 2: (Free Summon x4)

Or is it the more complicated, All effects for that turn pretend you are on your first turn and but since I actually spent 3 extra turns I am now down to total turns affected - 4 uses.

Turn 1: (Free Lunch, Free Summon x3) Turn '5': (40 MP Summon)

Answer 1

A turn is when you input your attacks/spells.

When you have negative BP you skip your turn for that character.

Eg:

turn 1:

Edea with 3bp free lunch and summon x3 free
Tiz with 1bp free lunch and summon x3 free
Ringabel with 3bp free lunch and summon x1 free

turn 2:

Edea with 0bp summon x4 free
Tiz with -1 no action
Ringabel with 2bp summon x1 free

turn 3:

Edea -2bp no action
Tiz with 0bp summon x4 not free
Ringabel with 2bp summon x1 not free

Answer 2

Brave lets you move multiple times in a turn.

If you do x4 Brave, you get to move 4 times in one turn, so:

Free Lunch -> Amp Strike -> Amp Strike -> Amp Strike

Will let you do x3 Amp Strike at 0 MP cost (even though Amp Strike is red, you have to select them manually).

If you can somehow move again the next turn, Free Lunch's effect would probably still be in effect.

For spells/abilities that don't have high costs like Amp Strike, you're probably better off just paying for the ability once and then using Mimic 3 times. This way you get to use it 4 times in a row, not have to Brave into -4 to get the most use out of Free Lunch.

Note: Mimic doesn't work for Specials, Rage, and Friend Summons.