This question claims that stock prices are considered "memoryless". Informally it is defined in the question to say that "past performance isn't an indicator of future performance". Technically memorylessness is a property of random variables, and again informally is used about probabilities: i.e. the fact that a coin came up tails last time it was thrown doesn't mean it is more likely to come up heads this time.
The trouble with this is that stock market prices are not random variables. However imperfectly, they represent the value placed on a company, and that valuation is going to be largely controlled by real world events. If a company's circumstances don't change, then a drop in its share price is going to be followed by a rise later. The prices can of course change when the company's circumstances change, but they aren't "memoryless" either. A company's future state is influenced by its past.
So: are share prices really described as "memoryless"? Is there a technical meaning of the term? What does it really mean?
EDIT:The other question now includes a link to this article which seems to equate the "memoryless" hypothesis with the "efficient market" hypothesis.