Serif font, by typographic definition, is a font in which the included characters have particular semi-structural elements or details at the ends of the lines or strokes that were used to outline a particular letter, number, or other symbol of the font. Basically, serifs are nothing but small decorative elements of the letters; however, there is a theory, claiming that a text printed in Serif font is easier to perceive for human eyes.
It is believed that Serif font history dates back to the times of Ancient Rome with the Roman alphabet and inscriptional lettering. That is why serif fonts are also known as Roman fonts. The most well-known representative of Serif font family is Times New Roman, which is familiar to everyone, who has experience of using Microsoft Windows and Office applications.
These days the range of Serif fonts applications is impressive: traditionally used for body text, serif fonts are commonly used in printed media, such as books, magazines, and newspapers. It is interesting to note that while Serif font texts are believed to be easier to read on paper, they are not always comfortable to read from the computer screen, especially if it is a small size font. People say that sans serif fonts (those without serifs) are better for onscreen presentations.
Typography experts define 4 subtypes in the Serif font family. They are old style, transitional, modern, and slab serif fonts. Old style fonts have the most traditional look, featuring low line contrast and diagonal stress. Serif fonts of modern style are characterized with extremely high contrast and vertical rather than diagonal stress. The characteristics of the transitional fonts with serifs are those in between the old and modern font styles. Finally, slab serif fonts are distinguished by their bold and square appearance.
If you are looking for free serif fonts, there are over a thousand of them at the leading font repository, called Fonts2u. You can either browse Serif font category or find the necessary font by defining its characteristics in the Fonts2u integrated font search engine.