1. Concerning how something is considered to be certain and without much doubt; very likely to be: The sky is covered with clouds and it is quite stormy outside, so it will probably rain.

Jane said, "I tried calling up Susan, but she didn't answer the phone, so she is probably out shopping."
2. Pertaining to how something is easy to believe on the basis of available evidence: Since Jack is respected among his colleagues and has the qualifications, he will probably be elected for the new position in the firm.