Deletion indicators tell the solver to remove certain letters in the fodder (the part of the clue the indicator works on).Some deletion indicators indicate to reduce the fodder, and can indicate to remove almost any letter(s) in a word (if done right) but generally they refer to the first letter, last letter (sometimes both first & last letter), middle letter(s) or either half of the fodder.
For example, phrases like 'topless' and 'uncrowned' indicate to remove the first letters.Phrases like 'almost', 'endless' and 'trimmed' indicate to remove the last letter.Phrases like 'lacking heart' and 'cored' indicate to remove the middle letter(s).Phrases like 'half cut' and '50%' indicate to remove either half of the fodder.
Deletion indicators also include departure and expulsion indicators. This is when we have some bits and pieces wordplay, for example "North = N", and we are removing it from some fodder.For example, "Silver only left out to cause heartbreak (5)", silver = AG, left = L. 'out' indicates departure i.e. remove L from ONLY. AG + ONY = AGONYBelow is a link to an extensive list of letter-deletion indicators.