I know that it means Minute of Angle and has ato do with accuracy. But can someone describe to me in idiot language what the definition of MOA would be?

Take a circle and break it down into degrees, 360, then break down each degree into minutes, there are 60. Therefore there are 60 MOA's in an degree.

The measurement is rounded to about 1" at 100 yds, 2" at 200 yds, etc.

taking the circle part, the shooter would be at the center point of the cicle.

Someone correct if I am worng or not giving enough info.

Mark

Ok, let me try.
Every angle is measured in graduations called degrees; 45, 90, etc.  One degree of angle can be further broken down into sixty graduations called "minutes".  Thus, one can have, say, 45 degrees, 20 minutes, or 187 degrees, 05 minutes.

For our purpose, one minute of angle= 1 inch (at 100 yards).  It is the measurement, from horizontal (zero) that one must raise the sight to equal a change of impact of 1 inch at 100 yards.  It can be front sight, rear sight, or the cross-hairs in the scope. Now, mind you most scopes have 1/4 minute adjustments, so to change point of impact 1 inch at 100 yards, one must move four clicks on the scope adjuster dial.
At 100 yards, one degree of adjustment would raise/lower the point of impact 5 feet! (60 inches), which is why we try for minutes, or even "seconds", of angle.

IHTH,
RB

Put another way:

An circle is divided into 360 equal partitions called degrees.  Each degree is divided into 60 equal parts.  The angle between these parts is a "minute of Angle".  In shooting terms, this corresponds to approximately 1 inch at 100 yards.  Therefore a rifle that is said to be "minute of angle accurate" or similar should be expected to land every round in a 1" group at 100 yards.  A scope that has 1/2 MOA or 1/4 MOA adjustment clicks will move the point of impact 1/2 inch or 1/4 inch per click, respectively.

In food terms:

Imagine a pizza 200 yards wide.  Divide into 360 equal slices.  Each slice is 100 yards long.  Divide that slice into 60 narrow slices.  Each narrow slice will be 100 yards long and 1 inch wide.

Mmmmm...  Pizza...  

Super nerd answer:

100 yds. x 2π = 628 yds circ
628 yds / 360 deg/circ= 1.75 yds/deg
1.75 yds/deg / 60 MOA/deg =  0.029 yds/MOA
0.029 yds/MOA x 36 in/yd = 1.05 in/MOA

Each Minute of Angle is 1.05 inches at 100 yards

Dammit!  No nerd smiley.  I demand a nerd smiley.  And a Tinfoil hat smiley.  And a pirate smiley.  And a Chuck Norris smiley.  And a ...  

Simple terms.

A dot.

A 1 MOA dot, covers a 1" circle at 100 yards.
A 4 MOA dot covers a 4" circle at 100 yards.
ect ect ect

They pretty much nailed it....

MOA is the 'universal measurement' of firearms equipment, weather it be red-dot size (an Aimpoint, for example, creates a 3moa dot wheras a Kobra projects a 1.5moa dot....) or weapons system accuracy (referring to a rifle as 'MOA out of the box means you should expect a 1" group at 100 without mods)...

These are the most common scenarios where it is used:

To rate group size (I shot a X MOA group today)

To rate weapons (The X-gun does sub-MOA out of the box, or 'With some work, I got (whatever) to shoot (whatever) MOA)

And to rate the size of scope reticles/dots....

As with all degree-related measurements, there's also the miliradian (mil) counterpart, as used in the 'Mil-Dot' scope system, and the M240 T&E..... Think of your compass - the black dial vs the red one...

Quoted: Simple terms. A dot. A 1 MOA dot, covers a 1" circle at 100 yards. A 4 MOA dot covers a 4" circle at 100 yards. ect ect ect

That's about as simple as it gets.

Quoted: Quoted: Simple terms. A dot. A 1 MOA dot, covers a 1" circle at 100 yards. A 4 MOA dot covers a 4" circle at 100 yards. ect ect ect That's about as simple as it gets.

thank god he came out. People using words like "math" and "partition" were making me throw up on the cat.

 <--- nerd smiley

Quoted: Put another way: An circle is divided into 360 equal partitions called degrees.  Each degree is divided into 60 equal parts.  The angle between these parts is a "minute of Angle".  In shooting terms, this corresponds to approximately 1 inch at 100 yards.  Therefore a rifle that is said to be "minute of angle accurate" or similar should be expected to land every round in a 1" group at 100 yards.  A scope that has 1/2 MOA or 1/4 MOA adjustment clicks will move the point of impact 1/2 inch or 1/4 inch per click, respectively. In food terms: Imagine a pizza 200 yards wide.  Divide into 360 equal slices.  Each slice is 100 yards long.  Divide that slice into 60 narrow slices.  Each narrow slice will be 100 yards long and 1 inch wide. Mmmmm...  Pizza...   Super nerd answer: 100 yds. x 2π = 628 yds circ 628 yds / 360 deg/circ= 1.75 yds/deg 1.75 yds/deg / 60 MOA/deg =  0.029 yds/MOA 0.029 yds/MOA x 36 in/yd = 1.05 in/MOA Each Minute of Angle is 1.05 inches at 100 yards Dammit!  No nerd smiley.  I demand a nerd smiley.  And a Tinfoil hat smiley.  And a pirate smiley.  And a Chuck Norris smiley.  And a ...

I knew how MOA applies to shooting, but I did not know the calculations behind it.  Very cool.

Actually the 1" at 100 yards is only one theory.

The other theory is that it is about 3 inches at 100 yards.  The people who support this theory are often seen bragging about the accuracy of their rifle with iron sights and surplus ammo.

Quoted: Actually the 1" at 100 yards is only one theory. The other theory is that it is about 3 inches at 100 yards.  The people who support this theory are often seen bragging about the accuracy of their rifle with iron sights and surplus ammo.

3" to 5" at 100 yards is good isn't it?  Hey I was using Iron Sights.