Over the years support for several different font types has been developed and evolved:
Raster Fonts (Legacy)
In a raster font each glyph is defined as a little bitmap designed for a specific resolution. They are not scalable like vector based fonts. Nowadays raster fonts are hardly used, except for specific tasks like booting your system, running MS-DOS-based applications and onscreen display in user interface elements.
Vector Fonts (Legacy)
Vector fonts contain glyphs that are defined as a set of points that define line segments. Although they can be scaled to any size, both quality and performance are poor compared to modern font types like those mentioned below. Your system might still contain one or two of these fonts but we strongly suggest to ignore them.
PostScript Type 1 Fonts (Legacy)
Adobe launched PostScript Type 1 together with PostScript Type 3 in 1984. This scalable font technology became very popular among desktop publishers, but is now being phased out.
TrueType is a scalable font technology designed by Apple Computer, available since 1991 (Apple's Macintosh System 7). Apple traded the technology with Microsoft and became available on Microsoft Windows 3.1 in 1992.
TrueType Font Collections
A TrueType Font Collection file is one or more TrueType fonts combined into one file. The TrueType fonts usually share information.
The OpenType font format is an extension of the TrueType font format, allowing support for PostScript font data. Technically there are two OpenType Font flavors; TrueType based (contains glyph outlines made out of lines and quadratic Bézier curves) and PostScript based (contains glyph outlines made out of lines and cubic Bézier curves). OpenType was developed jointly by Microsoft and Adobe to produce a hybrid between Type 1 and TrueType fonts, with additional features that work on Macintosh and Windows computers. OpenType fonts can include OpenType Layout Feature tables, which allow font creators to design better international and high-end typographic fonts.