Used to present one concrete case or illustration, often in explanations or when giving a representative sample.
一例を挙げて説明します。
I will explain by giving an example.
To give one example of success, this company is famous.
This is just one example of many problems.
As one example, I'll explain the changes of the four seasons in Japan.
This incident is an example of a social problem.
実例 refers to a real, concrete case that actually happened, whereas 一例 can be any single example, real or hypothetical.
具体例 emphasizes a concrete, detailed example used to clarify an abstract point, while 一例 simply means 'one example' without that emphasis on concreteness.
Compound of 一 (one) and 例 (example). The reading is the standard on'yomi combination.