Grades in school reports are expressed through letters followed or not by a sign like "plus" or "minus". Please how do you pronounce grades like A+ or A-, B+ or C-? I have also heard the phrase "straight A", what does it mean?
In the UK we say 'plus' for the + sign, and 'minus' for the - sign. I suspect it is the same in US schools.
In US English, a 'straight A' student is one who has achieved an A grades in every subject taken. We can use 'straight', mainly informally. to mean 'following one after another without an interruption; consecutive'. A football team that has played five games and won all of them could be said to have won 'five straight games'. Similarly a student who has scored As in every subject in a term, year, or during their school career has scored 'straight As', and is a 'straight-A student'.