Hi
Minor sins may be small matters which do not breach the rules of morality.
With regard to whether it is possible for the Prophets to commit minor sins, in Lawaami’ al-Anwaar al-Bahiyyah (2/214), al-Safaareeni quoted from Ibn Hamdaan who said in Nihaayat al-Mubtadi’een:
“They are infallible in conveying the commands and message of Allaah, but they are not infallible in any other regard. They may make mistakes, forget things, or commit minor sins – according to the most well-known opinion (of the scholars) – but they will not be approved for these mistakes.”
Islam QA - Do Prophets sin? Do they need forgiveness?
Minor sins are acts which are not major sins, and the major sins are clearly defined in the Qur'an and Sunnah with a threat of punishment. An example of a minor 'sin' is mentioned; Prophet Abraham lied to Nimrod by saying that Sarah is his sister [in faith], although she was really his wife. He said this because he knew that Nimrod would kill men who were married and take their wives as concubines.
Now according to the hadith, Abraham will say on the Day of Ressurection that he committed a sin, although it wasn't a major sin, and its likely that he was forgiven for it due to the necessity of the situation.
Whereas Abraham would never lie in order to get someone innocent killed for example. Since that would be a major sin.
So we see that lying is a major sin if it leads to a greater harm i.e. rape or murder, whereas lying in a smaller scaled scenario is a lesser sin (i.e. someone concealing a sweet and saying they don't have any.)
But even then, Prophets did not lie but may have said something with a double meaning in order that a greater harm does not occur. And if they (or even the believers) believed this was a (minor) sin on their part, Allah will forgive them - because He knows their situation well.