Abbreviations are shortened versions of words. They may be so common that they need no explanation (like km and etc.); they may be common within certain fields (like μg for ‘microgram’ or viz. for ‘videlicet’) and whether such abbreviations need to be explained or not depends on the audience for the text. Abbreviations may also be specific to the text at hand, in which case they always need to be explained, preferably the first time they are used. Note that in the following examples, the boldface is used only to highlight the abbreviation; abbreviations are not normally highlighted in text.
The recent results (e.g., Gerhardt et al. 2013) are encouraging.
When reporting common measurements, the full stop is often omitted, except of course if the abbreviation is the last word in a sentence.
We used 250ml of water per trial. This drive has 100Gb of storage. The distance travelled was 153km.
Acronyms are a special type abbreviation in which the first letter from each word is used. Often acronyms do not need to have full stops after each letter, although they can (such as the U.K. and the U.S.).
In 2012, the National Veterinary Institute (SVA) started a national project called Myggjakten in order to collect mosquito DNA.