Core Booster
A Booster Pack is a package consisting of a few cards. OCG Booster Packs have around 5 cards in them, and TCG ones includes between 8-12 cards. TCG Booster Packs are guaranteed at least 1 Rare and/or holo card, while OCG Booster Packs are not always guaranteed a Rare card. Booster Packs can be bought at most game stores and at some general/department stores.
Video Games
In Video Games, player can purchase a booster pack by defeating an opponent (eg. Yu-Gi-Oh! The Eternal Duelist Soul) and buying at store (eg. Yu-Gi-Oh! Tag Force).