A stock split causes a decrease of market price of individual shares, but does not change the total market capitalization of the company: stock dilution does not occur.
[1] A company may split its stock when the market price per share is so high that it becomes unwieldy when traded.
Stock splits are usually initiated after a large run up in share price.
Some companies avoid a stock split to obtain the opposite strategy: by refusing to split the stock and keeping the price high, they reduce trading volume.
If some investors are unable to recognize that a split stock should trade at a lower price than before the split, the result can be a temporary increase in demand and the share price.
Investors will sometimes receive cash payments in lieu of fractional shares.
Other common reporting nomenclatures are ‘x-y’ and ‘stock dividend’ of [=]y-x.
As a result, when looking at a historical chart, one might expect to see the stock dropping from $50 to $25.