planar molecules

can someone explain what is meant by a planar structure?? i thought its where alll the angles of the molecule are 120 but it says methanoic acid has a planar structure but it has a 104.5 bond angle :/

q2 does replacing the H in a c-H bond with a halogen make the bond stronger or weaker?? is it stronger due to larger difference in electronegativity????

All of the atoms are in a plane.

what? could u explain more pls...

what? could u explain more pls...

Same plane, i.e. they're flat. All angles don't have to be $120^{\circ}$, no. That's only the case when the molecule is trigonal planar.