MATLAB fir2 - npt and lap
npt is the number of frequency points that are used to define the desired frequency response. It's the length of the inverse FFT that is applied to the frequency domain data. It defaults to $512$ points, but if you want to design very long filters (with many taps) then you should choose a larger number.

lap defines the width of the transition band, if there is one. There is a transition band if there are two equal frequencies specified in the vector f, where a step in the desired response occurs. The wider the transition band the smaller the approximation error in the pass bands and stop bands, so there is a trade-off between steep transitions and approximation errors in the pass bands and stop bands.