Uniform Thickness

• Block fonts have strokes that are the same thickness. Strokes are the main lines and curves that form the shape of the letter.
  
  

Square Corners

• Block fonts almost always have squared-off corners on the edges. This doesn't mean there won't be any curves. A letter "S" or "O" is hard to make without any curves, though some fonts achieve this. But block fonts are more likely to have lots of straight lines and sharp corners than other fonts.
  
  

Slab Serifs

• Fonts may be classified as serif or sans serif, meaning that they have or don't have serifs, little strokes or lines at the ends of the long, main strokes (the text you're reading now is sans serif). If block fonts have serifs, these serifs are most often shaped like squares or rectangles and are known as slab serifs.
  
  

Capital Letters

• Many block fonts contain only capital letters. They may also use what is known as "small caps," which means that letters normally typed as lower-case letters would instead be formed as capital letters, but these letters would be smaller than standard capitals.
  
  

Readable

• Block letters are not usually meant for body text. Instead, these types of bold, square letters are suited for advertisements, signs and other places where relatively large type is needed. Another use for block letters is in typing easily-read school materials for early readers. In this case it would technically be considered body text, but it would be much larger than normal body text.