This is the 754th most frequent Chinese word.
实
Real; true; solid; practical; actual.
In this sentence, "实" is used to denote something that is reliable and precise.
这份报告内容很实在，信息详实。
This report is very reliable and contains detailed information.
Here, "实在" is an adverb meaning 'truly' or 'really', used for emphasis.
他实在太忙了，没有时间休息。
He is truly very busy and has no time to rest.
The word "实" in "实验" refers to something practical or relating to actual practice or real-world conditions.