These are gameplay hotkeys and can be re-bound by going to Settings → Controls. The keys listed here are the defaults.

Throw ( Q ) — Throws your currently active item away. Note that this will throw the entire stack (unless holding Torches, as they provide light even as a tossed item).

Quick Heal ( H ) — Consumes the first healing item in your inventory.

Quick Mana ( M ) — Consumes the first mana restoring item in your inventory.

Quick Buff ( B ) — Uses items that cause buffs or debuffs, unless their associated buff is already active. You can have a maximum of 10 (de)buffs, and this hotkey will stop when that number is reached.

Grapple ( E ) — Uses your Grappling Hook, if you have one equipped.

Mount ( R ) — Summons your Mount, if you have one equipped.

Auto Select ( Left Shift ) — This is a very context sensitive action that basically does 3 things. Tool selection : If you mouse over a tile or an object, you'll automatically select the appropriate tool, even if it's not in your hotbar. For example, hovering over a Stone Block and holding Shift will cause you to select a Pickaxe or Drill. Trashing/selling : Clicking on items in your inventory while holding this will transfer them to the trash slot. If an NPC's shop window is open, you'll automatically sell that item to the NPC instead (even if it has no value). Lighting : If you mouse over nothing, holding Auto Select will make you hold a light source, if you have one. Close up, this will be a Torch or a Sticky Glowstick, but if you move your cursor farther away, it'll be a normal Glowstick. Underwater, it'll always be a type of Glowstick. Make use of this extensively.

Auto Target ( Left Ctrl ) — Toggles Auto-Targeting mode for tools. Tools will automatically target the closest block in the direction given by the cursor.

Favourite Item ( Alt+Left Click ) — As of version 1.3, items can be favourited. Favourited items cannot be quick-trashed, quick-stacked or deposited.

The following are mostly undocumented and hardcoded (i.e., can't be changed):

Fullscreen ( Alt+Enter ) — Enters and leaves fullscreen mode without having to leave the current world.

Switch lighting ( F9 ) — Toggles lighting mode between Color, White, Retro, and Trippy (can also be done from the video settings).

Show FPS ( F10 ) — Displays frames per second in the lower left corner; the number in brackets is liquid debug data of some description.

Hide UI ( F11 ) — Toggles all user interface elements, including the cursor. This is useful for taking clean screenshots.

And, last but not least:

Screenshot ( F12 ) — Takes a (JPEG) screenshot. This isn't technically a Terraria hotkey, but courtesy of the Steam overlay. Can also be re-bound to another key in your Steam settings.