Learner's definition of SPECULATION
1 : ideas or guesses about something that is not known
He dismissed their theories as mere speculation.
The book is just a lot of idle speculation about the future.
There is speculation that he will run for president again. [=some people think that he might run for president again]
2 [noncount] : activity in which someone buys and sells things (such as stocks or pieces of property) in the hope of making a large profit but with the risk of a large loss