In options trading, a vertical spread is an options strategy involving buying and selling of multiple options of the same underlying

Underlying

In finance, the underlying of a derivative is an asset, basket of assets, index, or even another derivative, such that the cash flows of the derivative depend on the value of this underlying...

 security, same expiration date, but at different strike prices. They can be created with either all calls or all puts.
The term originates from the trading sheets that were used in the open outcry

Open outcry

Open outcry is the name of a method of communication between professionals on a stock exchange or futures exchange. It involves shouting and the use of hand signals to transfer information primarily about buy and sell orders...

 pits on which option prices were listed out by expiry date & strike price, thus looking down the sheet (vertical) the trader would see all options of the same maturity.

Bull vertical spread

Bull call spread and bull put spread are bullish vertical spreads constructed using calls and puts respectively.

Bear vertical spread

Bear call spread and Bear put spread are bearish vertical spreads constructed using calls and puts respectively.