Draw a card
To draw a card (ドロー, Dorō) is to take the top card of your Main Deck and add it to your hand.
Drawing a card is a form of “adding a card from the Deck”. If "Blackwing - Breeze the Zephyr" was drawn by a card effect, then you can Special Summon it. Because of this, the card "Thunder King Rai-Oh" had to clearly make an exception in its lore, and the card "Drastic Drop Off" had to clarify that drawing is considered adding a card to the hand.
Every turn during your Draw Phase, you normally draw one card from your Deck. Some effects also let you draw cards, such as "Pot of Greed", "Royal Magical Library", and "Jar of Greed". (As of March 21st 2014 in the OCG, however, the player who takes the first turn will be unable to draw during that turn only.)
Incidentally, there is a difference between “number of draws” and “number of cards drawn”. The number of draws refers to the number of times any number of cards are drawn, like when resolving "Hand Destruction", as both players draw 2 cards at once. However, cards like "Heart of the Underdog" only facilitate drawing one card per effect activation, but the effect can activate any number of times.
If you are unable to draw a card because you have no cards left in your Deck, you lose the Duel.
