It simply means this:
They find you attractive. You are triggering an uncontrollable physical attraction towards you.
They could be trying to check out your ass, could be nicely or not-so-appropriately blinded by your cleavage, just watching you move, and/or enjoying any part of you which is their preference area to be sexually attracted to the most.
Consider yourself a highly attractive woman to him and all those that do the same.
Guys will also look your way to catch your eye - they're trying to make eye contact to gauge your interest in them. Once the eye contact is secured, they may or may not approach you (that depends on the guy and the situation AND whether he's a type one or type two ) AND regardless of all that they still want your body language approval of some sorts saying it's okay to talk to you.
They rarely if ever look a woman's way they don't find attractive because they don't want to catch the "wrong" woman's eye and have to deal with the consequences of her just maybe believing he's into her.
The difference between the two types of guys as their looking at you:
Type ones generally have a purpose of looking at you - to secure the approach of you or establish some level of mating ritual dominance. Something you can read more about here:
This type is more likely to approach you and start a conversation. He also wants to get caught so eye contact can be made.
Type twos have the same goal in mind BUT they rarely if ever act on it. They look because they like what they see but won't do anything about it.
Since they barely will move forward and do something after eye contact - this type doesn't want to get caught and tends to avoid making direct eye contact.
Both are aware of what they're doing and why and have conscious control over doing it BUT neither has control of what they're feeling while they're doing it.
The only anomalies or variance from what is listed above is if they guy doing the looking is in a relationship.
He's still feeling attracted to you and it is still the reason why he's looking but approaching or starting a conversation is not the purpose.
Most are simply basking in what they find beautiful and enjoying the feelings of attraction.
There are a few exceptions to all this looking which goes beyond the scope of attraction and I'll lightly cover a few of them for you.
Guys will often look my way too and I'm not talking about gay guys just checking me out.
It's to either:
Establish dominance in a group.
When a male enters a room or a place he may scan and make eye contact with many people to see where hit fits within the group. If he catches your eye and it feels like he's looking at you - most of the time he's not (even if he does it a few times) - man or woman - he's trying to establish his dominance or lack of dominance in the group.
Protect and secure their environment.
Similar to establishing dominance he'll look around to find safety in the group. He may then position himself in an area where he feels safe and gives him the opportunity to protect himself.
The security or protection he's looking for is not always from physical attacks unless the area merits it - mostly it's a social anxiety thing and he wants to feel safe and comfortable as he scans the room for potential problems.
Again - it may FEEL like he's looking at you and is finding you attractive but it's not always the case making it easy to misread why it's happening to you. (Especially if it happens a lot.)
Show social awareness.
As he looks around where he is, eye contact is often made with several people to show them he's socially aware of his environment, wants to make others feel more comfortable being around him, and is opening up a sub-textual line of communication to be used later.
The purpose is to make the progression from entering to starting a conversation with a man or woman (friend or stranger) go more smoothly.
It's typically the trait of a guy who is socially exceptional.
I realize there are a few other circumstances where a guy might be looking at you for reasons which are not always so nice BUT based on my experience and knowledge in this area - they are very rare and not worth mentioning today.
While trying to figure out why a guy is looking so much try to keep everything in context. Circumstance and situations will always be slightly relative to why or if it's happening.
How you believe others see or perceive you will also have a small impact as to why you're thinking it's happening. It's best to remain impartial IF you're to see the real reason of it happening.
The most common reason is listed above and I believe it's the best answer that fits...
When a guy is looking at you - he's feeling attracted to you.