Question

Electrons in what are held loosely and in electrons are held tightly by what

Answer 1

Electrons are held loosely in conductive material such as metal, and are held tightly in non conductive material such as rubber

Answer 2

As already explained by @Thefaceless that electrons are more loosely held in conductive materials than the insulators and semiconductors I would like to add the notion of band gap
In metals the band gap between valence band and conduction band is less and usually overlapped hence electrons can move freely from valence to conduction band and are less tightly held while in insulators the band gap is very high so we have to provide large amount of energy to move an electron from valence to conduction band and hence could be said very strongly held..!

Answer 3

As explained by others here...in a single atom case it's bound by ionisation potantial and in a body it's bound by work function...actually work function is a aggregated effect of ionisation potantial(for an analogy lonely behavior and group behavior are different :) )..So if this is less material is good conductor otherwise semi or bad conductor..