Istighfaar (seeking forgiveness) is of two types, depending on whether the word is used alone or is accompanied by the word tawbah (forgiveness). When it is mentioned alone, it essentially means the same as tawbah. The two words are interchangeable, each carrying the meaning of the other, when mentioned separately.
When the two words are used together, istighfaar means seeking protection from the evil of what is past, and tawbah means returning to Allaah and seeking protection from the evil of one’s own bad deeds which one fears may lie ahead in the future.
Istighfaar and tawbah are among the pairs of words which the scholars say convey one another’s meanings when used alone, but which have their own separate meanings when they are used together. And Allaah knows best.