{fontsize} is about selecting a document's standard font size (with class options like 12pt), changing relative font sizes within a document (with macros like \small or \large), and defining or modifying {macros} related to font sizes.
fontsize is about selecting a document's standard font size (with class options like 12pt), changing relative font sizes within a document (with macros like \small or \large), and defining or modifying macros related to font sizes.
Packages providing fontsize support include relsize and anyfontsize. The memoir document class also supports a wide range of font sizes by default.
