Safari is a Swahili word meaning long journey. It originally came from the Arabic word safariyah, which just means a journey. Swahili has a large numer of words of Arabic origin due to many centuries of contact between East African and Arabic communities and traders.
In Swahili the word can be used for any type of long journey, eg on foot or by public transport. However, in modern English it usually means a special trip involving, especially, African wildlife. Until recently a safari in English usually meant a big-game hunt trying to shoot a lion or other large animal, but nowadays many tourists go on 'safaris' just to see and take pictures of African wild animals and experience the outdoor life (though usually under the protection of rangers and other local guides).
It is usually thought that the first person to use the word safari in English was the 19th century explorer Sir Richard Burton.