Proximity operator is used when the search terms need to be within a certain distance from each other. It defines how many words there can be between two words. Proximity operators are database specific and all databases don't use them. Check the functioning of the proximity operators in the Database quick guide.
For example, W/2 in the Scopus databases looks for references with search terms max. two words apart, in any order. Scopus 27.7.2018.
The number used with a proximity operator defines how wany words in maximum there can be between the search terms. You can use the following table as a rule of thumb:
|Term distance||Good for finding...||Example|
Useful for finding synonymes for a phrase. Sometimes works also in the databases where automatic stemming or lemmatisation doesn't work inside the quotation marks.
(drinking OR potable) W/0 water
|1-5||The words within the same phrase.||energy W/3 policy|
|5-15||The words within the same sentence. Useful especially for full text search.||erosion W/10 vegetation|
|20-50||The words within the same paragraph. Useful for full text search.||healthcare W/30 Finland|