From Longman Dictionary of Contemporary Englishtouch on/upon something phrasal verbDEAL WITHto mention a particular subject when talking or writing The report touches on the relationship between poverty and poor health. These issues were touched on in Chapter 2. → touch→ See Verb table
Examples from the Corpus
touch on/upon • Much of this I have touched on already.• That topic was only touched upon by the hon. Member for Gateshead, East.• A touch on her shoulder made her spin around.• Reach out and put the touch on some one.• We are in touch on that.• Positive thought for the day Earlier today we touched on the fact that other members of your family may also have goals.• Martin Karplus of Harvard University touched on the issue at a conference in honour of Pople in 1990.• When everything touched upon turns wry, fluffy or romanticized, the menace itself seems trivial. 