Stock split vs reverse split: what is the difference?
They are the same operation pointed in opposite directions. A forward split(usually just called a stock split) divides your shares into more, cheaper ones. A reverse split merges them into fewer, pricier ones. In both cases your total value and your ownership percentage are unchanged at the moment it happens.
Side by side
Forward 2-for-1: 100 shares at $200 becomes 200 shares at $100.
Reverse 1-for-10: 100 shares at $2 becomes 10 shares at $20.
Same pizza, different number of slices, both times. The arithmetic is trivial. The signal is where they differ completely.
Why the reasons are opposite
A company does a forward split because its price got high, usually after a long run of success, and it wants the shares to feel accessible to retail buyers and options traders. It is a confidence move, which is why forward splits are often greeted well.
A company does a reverse split because its price got low, and typically because it must: exchanges delist stocks that trade under $1.00 for too long. It is a compliance move, and the market reads it as such. That is why two mathematically identical events land so differently.
What to check on each
On a forward split there is usually not much to investigate. On a reverse split there are two things worth five minutes: whether the company has done one before, and whether the share count grew back afterward. Repeat splits with a regrowing share count is the serial-diluter pattern, and it is visible on the cover pages of successive quarterly reports.
One naming note that trips people up: forward splits are written "2-for-1" or "3-for-1" (you get more), reverse splits "1-for-10" or "1-for-20" (you get fewer). The small number first means reverse.
Related reading: what a reverse split is and why penny stocks keep doing them, ratios explained with the math, and whether they are good or bad.