Comparisons between "serif fonts" and "sans-serif fonts" generally compare Times-Roman or Times New Roman against Helvetica or Arial. The presence of serifs on the former and lack of them on the latter, however, is not the most noticeable difference. A more significant difference is the fact that the former fonts are drawn with a mixture of wide and narrow strokes, while the strokes in Arial are of relatively-uniform width. This is most noticeable in letters like "V" which include strokes in both diagonal directions; in Helvetica, the strokes in both directions match, while in Times-Roman they are very different.
Is there a term which would distinguish a font like Belleza:
from Helvetica, or Coustard:
The distinction is perhaps quantitative rather than qualitative, though for fonts where the "V" has diagonal lines with roughly-equal angles, there's probably a pretty clear partition between fonts where the strokes are of equal weight, versus those where they are substantially unbalanced.