A colon is used:
- to show that whatever follows (a complete thought, a phrase or a word) is an explanation or expansion of what has already been said
There was only 1 explanation: she did not want to be seen.
- to introduce a quotation or a list (see also Quotation marks and Lists); however, do not use a colon before a run-on list within a sentence
Threats to biodiversity include:
- habitat reduction
- pest animals
- climate change.
but
Threats to biodiversity include habitat reduction, pest animals and climate change.
- to separate a subtitle from a title
Staying healthy: preventing infectious diseases in early childhood education and care services
Developmental Leadership Program (DLP) policy brief: the role of local leadership processes and coalitions in development
- to separate the elements of a ratio (no spaces)
- to separate page numbers from other components of references cited in the text or listed in the reference list (see References)
Smith (2014:12) Journal of Chemistry 3:4–18
- to separate hours from minutes in times of day (a full stop can be used as an alternative)
- to separate hours, minutes and seconds
9:15:30 [9 hours, 15 minutes, 30 seconds]
- in some specialised scientific terminology (eg some chemical names, and chromosome and gene terminology).
