Passing from one topic to another.
Some days he allowed himself to write long discursive essays in his diary instead of his usual simple reporting of the day's events.
The Latin verb discurrere meant "to run about," and from this word we get our word discursive, which often means rambling about over a wide range of topics. A discursive writing style is generally not encouraged by writing teachers. But some of the great writers of the 19th century, such as Charles Lamb and Thomas de Quincey, have shown that the discursive essay, especially when gracefully written and somewhat personal in tone, can be a pleasure to read.