I recommend to ammend the above answers using the following descriptions
PICA
Pica Typographic unit of measurement in the anglo-american point system. One pica is 1/72 Inch (0,351 mm) and equals 12 pica points. The didot equivalent of a pica is a cicero. A standard unit of measure in newspapers. There are 6 picas in one inch, 12 points in one pica.
PICA POINT
Pica Point 1/12 of a pica
POINT
996 points are equivalent to 35 centimeters, or one point is equal to .01383 inches. This means about 72.3 points to the inch. We in electronic printing use 72 points per inch
1 point (Truchet) = 0.188 mm (obsolete today)
1 point (Didot) = 0.376 mm = 1/72 of a French royal inch (27.07 mm)
1 point (ATA) = 0.3514598 mm = 0.013837 inch
1 point (TeX) = 0.3514598035 mm = 1/72.27 inch
1 point (Postscript) = 0.3527777778 mm = 1/72 inch
1 point (l’Imprimerie nationale, IN) = 0.4 mm
EM
An old printing term for a square-shaped blank space that’s as wide as the type is high; in other words, a 10-point em space will be 10 points wide.
EN
Half an em space; a 10-point en space will be 5 points wide.
DPI
The number of dots per inch a printer prints. The higher the dpi, the finer the resolution of the output.
PIXEL
The smallest dot you can draw on a computer screen
CPI
Counts per inch for Mouse properties and The number of horizontal characters that will fit in one inch for Printer properties
PITCH Alias CPI
Pitch describes the width of a character. Pitch equals the number of characters that can fit side-by-side in 1 inch; for example, 10 pitch equals 10 characters-per-inch or 10 CPI. Pitch is a term generally used with non-proportional (fixed-width) fonts.
TWIPS
A twip (derived from TWentieth of an Imperial Point) is a typographical measurement, defined as 1/20 of a typographical point. One twip is 1/1440 inch or 17.639 µm when derived from the PostScript point at 72 to the inch, and 1/1445.4 inch or 17.573 µm based on the printer's point at 72.27 to the inch
Additional Units:
LPI
The number of vertical lines of text that will fit in one inch
PPI
Thickness of paper, expressed in thousandths of an inch or pages per inch.
or sometimes no of horizontal pixels closely printed or displayed per inch.
FONT SIZE
Font size or Type size is the baseline distance for which the font was designed. A font should normally be identified and selected by this size, because the intended baseline distance is much more relevant for practical layout work than the actual dimensions of certain characters.
FONT HEIGHT
Font height is the height in mm of letters such as k or H. Typically, the font height is around 72% of the font size, but this is of course at the discretion of the font designer.
X-HEIGHT
x-height indicate typesize of lower-case letters excluding ascenders and descenders (from the height of the lower-case x)
H-HEIGHT
h-height or cap height refers to the height of a capital letter above the baseline for a particular typeface. It specifically refers to the height of capital letters that are flat—such as H or I—as opposed to round letters such as O.