A property is a key-value pair associated with an entry. Properties can be set so they are associated with a single entry, with every entry in a tree, or with every entry in an Org mode file.
There are two main applications for properties in Org mode. First,
properties are like tags, but with a value. Imagine maintaining a file where
you document bugs and plan releases for a piece of software. Instead of
using tags like
:release_2:, you can use a
:Release:, that in different subtrees has different
values, such as
2.0. Second, you can use properties to
implement (very basic) database capabilities in an Org buffer. Imagine
keeping track of your music CDs, where properties could be things such as the
album, artist, date of release, number of tracks, and so on.
Properties can be conveniently edited and viewed in column view (see Column view).