In standard English the primary meaning of the adjective bold is ‘brave, courageous, unafraid, daring’. This can shade into a related, negative sense of impudence, brazenness, or presumption. Another common sense is ‘visibly prominent, distinct, strong, or clear’, often associated with lines or colour. For nuance, compare the definitions by M-W, AHD, Oxford, Macmillan, Cambridge, and Collins.
When I first learned the word, though, it was in none of these senses: it meant ‘naughty, mischievous’. If I heard someone (including myself) described as bold, it meant they were misbehaving – or maybe being playful in a cheeky way. This is a very common usage in Irish English but absent from standard English; there’s no mention of it in the OED.
The sense is so intrinsic to the word in Ireland that when I read this line in Swing Time by Zadie Smith last week, I had to read it twice to be sure of the intent: