
Thurgyn |

Spell levels can be referred to as spell slots. A 1st level spell uses a 1st level spell slot except for when metamagic feats alter the spell, such as Empower (+2 spell level) which causes a 1st level spell to occupy a 3rd level spell slot.
Caster level refers to how powerful of a caster you are and is different from character level (total of all class levels).
For example, lets say your rogue/wizard is 4 levels Rogue and 3 levels Wizard and casts Magic Missile, a first level spell. You would cast 2 missiles for 1d4+1 because your caster level is 3 while your character level is 7 thereby making you unable to cast the four missiles allotted to caster level 7.
Hope this helps and isn't too wordy.

Quatar |

Level when in reference to spells usually refers to Caster Level. Level in the context of class abilities usually refers to class levels. Levels refered to outside a specific context usually refers to character level.
However usually character level is spelled out almost in every instance.
Spell level also is usually spelled out. I don't remember a single instance where they just say "level" and mean spell level. Except when they say "the level of the spell" or something, which is nothing else but a longer way to say "spell level".