Piece Dictionary

Brace yourselves, this is a long one!
You may be reading the building tutorials thinking "What on earth is a 2x3 angled plate or a 1x1 brick with two side studs?" This post will show you the names of common and not so common LEGO pieces.
First off, bricks and plates.
Here are some examples of plates. Left to right, 6x8 plate, 2x6 plate, 2x4 plate and 1x2 plate. As you might have guessed, the numbers refer to the number of studs it has lengthwise and width wise. Three plates stacked is the height of a brick.

Here are a couple examples of bricks. A 1x1 brick and a 1x2 brick.

 Bricks can be rounded too, not just square. So can plates. Plates are basically just thinner versions of bricks.
Here is a 2x2 brick and a 2x2 rounded brick. Below that is a 1x1 brick and a 1x1 rounded brick. We like to call the 1x1 round bricks soda cans because we pretend they are minifigure soda cans.

Now for tiles. Tiles are similar to plates, except they don't have any studs on top. They are smooth.
Here are some examples of tiles. A 1x2, 1x1, 2x2 and 1x6 tiles.

This piece might have an official name, but for now we just call it a
Stool

 This is an example of a sloped brick.
2x3 Sloped Brick

 This is a brick, but with an obvious difference.
1x2 Brick with hole

 This is a fun piece. 2x2 Turntable I like to attach it to chairs to create a spin-y chair. Whoo-hoo!

 There are lots of different types of hinges. This is a Hinged 1x4 plate This type of hinge comes in bricks too.

 These pieces can be used as hinges. A 1x2 plate with two vertical clips and a 1x2 plate with bar clipped together make a good hinge. We used the bar and clip method a lot in creating the dragons.

Here is a 1x2 plate with bar and a 1x2 plate with handled bar Slightly different.

 This type of hinge is called a Click hinge because of the clicking sound it makes when you move it.

 This brick has a hinge built into it, which is why its called a Hinge brick As I mentioned before, we refer to them as Wal-E eyes because my Dad built a LEGO Wall-E model and used this piece as his eyes. (You know, Wal-E, the little robot from the movie Wal-E?)

 These pieces are called (left) a Mug and (right) a Goblet I used the goblet piece in my LEGO saxophone.

 Another piece with a clip. This one is called a 1x1 tile with a vertical clip

 These are a couple examples of Radar Dishes A medium one and a small one. Lots of uses!

 This is a LEGO Technic piece. This piece is known as a LEGO Technic Connector You can put it in holes like the one in the 1x2 brick with hole I showed you earlier. Very useful for makes moving things. I used it a lot in a LEGO Ferris wheel I built once.

 This is a 1x2 Grille My brother used it for the front of his LEGO Truck.

 This piece is a 2x2  round sliding plate. Mainly used on the bottom of a hovercraft vehicle to make it glide. It is actually upside down in this picture. The smooth, rounded part is the bottom and it has four studs on top to attach it to the bottom of something.

 Here's a 1x2 sloped Grille

 This is a useful little brick. The Headlight Brick It is used in several of our creations, for example, the LEGO Gumball Machine. Notice the little ridge on the bottom.

 This piece is very similar to the head light brick, except the stud on the front sticks out. In the headlight brick, the side stud is sunk into the side a bit. It's a 1x1 brick with one side stud

This is a 1x1 brick with two side studs

 This is a 1x1 brick with four side studs I used it for the LEGO lamp.

 1x1 Cone This one is a transparent cone.

 2x2 Round plate

 Here is a 1x1 plate with vertical clip and a 1x1 plate with horizontal clip

 Horn piece We use these a lot for dragons

 You saw this piece in my heart necklace post, it's a 2x3 curved plate with hole

 Some pieces with obvious names, Tree and Chain

 Used for scout ships, it's a 1x1 plate with ring

 Some car parts, left to right Mudguard , Car Seat and Steering wheel

 1x1 round plate A very useful piece.

 Lever Nice for switches and controls on various gadgets.

 Ladder It can be used for more than climbing, seen as the grille on the kid car.

 2x2 dome Yes, that is R2-D2's head

 Jumper plate

 Here are some slopes, a 1x2 slope and a 1x1 slope The 1x1 slope had a post all to it self!

There are a wide range of arched bricks. This one is a 1x4 arched brick

 Some debate on this one. Either Antenna or Hinge Rod (Also Thingys. See the LEGO Adventures Of Clutch Powers on Netflix to get that joke.)

Another LEGO term you might see is SNOT. It is a building technique. The letters stand for Studs Not On Top. It's a building style in which you build any way but up! (Clearly, the acronym was invented by a boy.)
I hope this was informative. Now if you are looking for a certain piece, you can say "Pass me the 2x3 gray plate." Instead of "Hey, can you give me that gray thing over there, no, not that, no, um, oh, yeah that thing. Thanks."