The term Black July was basically the beginning of the civil war in Sri Lanka. The name refers to the riots in Sri Lanka that took place in July of 1983. The riots started out as a response to a horribly deadly ambush that took place on 23 July 1983. It was headed by the Liberation Tigers of Tamil Eelam. That was a Tamil militant group that existed at that time.
They slaughtered 13 Sri Lanka soldiers in the fight and the Sri Lanka people simply weren't going to tolerate it. By the end which was 7 days, between 400 and 3000 people were dead and around 150,000 were homeless. Countless homes and businesses were destroyed too. It was a horrible thing but ultimately, Sri Lanka gained their independence.