What does pt in 18pt, 12pt mean?
To produce this in most typesetting or word-processing systems, the author would have to decide what layout to use, so would select (say) 18pt Times Roman for the title, 12pt Times Italic for the name, and so on.

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Here 'pt' means 'point', short for "typographic point". I think that, despite having been chosen to label several units of measure over the years, nowadays this name mainly refers to the "PostScript point" unit of measure, the one used in desktop publishing, defined as 1/72 of an inch or, approximately, 0.3527 mm.

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pt is short for point and refers to the size of a font. It is one of the most commonly used measurements but not the only. It is mostly used in printed documents where as px (short for pixels) is the size used for websites and other screen based typography.