wht does it mean when a fret note is in partenese for example 3 (0) 3
A grace note, it's essentially a very quiet note that's only played very briefly
It refers to a ghost note, which is played quite softly. It is called a ghost note, not a grace note, as LepperAffinity, said.
There aren't a lot of conventions in Tabs, but it often means an accidentally played note, something that you hit by accident on the way to another. It could be a grace note or it could have a value. It could be a natural harmonic, though natural harmonic are usually written <5>. Also, you can have a natural harmonic on an open string.