Head toss, what does it mean?

I've been watching my horse very closely lately, and I've noticed that she often tries to tell me something with a head toss.
I do not mean while we're riding (she never tosses her head then) but rather when she's loose in the pasture. It is definitely a horse-language thing and I want to figure it out. I have noticed several variations of this movement but it always involves flicking the head in some manner. All of the horses seem to do it, and when my horse tosses her head to another horse they respond, so I know that it is used for communication.
My Monty Roberts book briefly mentions that a head toss can mean "I didn't mean to do that" but I cannot imagine that all of the horses I see would be saying that all the time!

I am really curious about this now. I want to know what my horse is trying to tell me when she does this. Does anyone have any clue as to what it means? Or if you don't, could you tell me in what situations you have seen your horse toss his/her head? I've got to get to the bottom of this!

(I'm sure that after watching them in the pasture for long enough I will be able to figure it out, but I thought this might help to speed up the process by giving me something to look for)

Here is a (very dusty and old) picture for reference. Sorry it's so big, I made it smaller but it sill displays in the same size.

As you said it is communication. I think from watching mine it can mean a few different things. Mine will do it in anticipation of feeding, or getting out of the paddock. Maybe excitement? Another will do it to the other horses to make them move or maybe "I'm dominant"? I think it just depends on the situation. I wondered the same thing for awhile but these are the only things I can come up with.
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What breed is she? No offense to anyone - but Arabs tend to have more of an attitude and love to do the head flick rather frequently.

That being said - my three year old foundation QH filly has the MOST attitude with her head of any horse I have ever seen. Loose, on the line, under saddle, etc - always expressing her self. Has from day one!

Mls, believe it or not she's a paint with mostly halter bred quarter horses in her pedigree, haha. But she looks like an arab. She also has a lot of attitude, and like you said I do think that is part of the reason why she does this so much.

I also agree that it does seem to have a lot to do with excitement, mbender. I have seen her do it when she is not excited too, so I'm confused about that part. It is interesting that you mentioned that your horses shake their heads before being fed. I am never around when my horse is fed so I didn't know about that.

She is very cute

Thank you :)

When my mare does it while out and about in the pasture it is either a: she is excited and fired-up, or b: she is warning someone to get out of her "bubble", haha!

Our younger mares toss their heads at each other when they want to play...like "let's go run around" or "chase after me".

My standardbred does this primarily to indicate she's mildly pissed off or frustrated about something. Could be that she touched the electric fence by accident, could be that the other horse is going out and she's not, could be that I chatised her for something from a distance, could be that I went outside and didn't visit her. Once she wiped out running around a corner in the field and flipped her head about that. Always seems to be an outlet of negativity for her but not truly angry.

My mare does this all the time and mostly when she is turned out or during feeding time. Both very exciting times. I think it is just a playful gesture.