generally; as a rule; on the whole
Used to make a broad statement that applies in most cases, often followed by a conclusion or observation. Slightly formal but common in everyday speech.
Generally speaking, Japanese summers are hot and humid.
His opinions are generally correct.
一般に states a general tendency plainly, whereas 概して is a slightly more formal way of saying 'on the whole,' often allowing for exceptions.
概して is a formal adverb for 'generally' that overlaps with the adverbial sense of 一体 (as in 一体に), but 一体 also has noun, counter, and emphatic-question uses that 概して lacks.
The adverb is the て-form of the literary verb 概す, “to generalize” or “sum up.”