This is what the statuses mean to me:
Personal Note in your contact list: Giving people insight in what you are up to that day or point in time, or could be the sharing of a thought process.

1. Available

Being the standard or default status. Indicates that someone is available for phone calls, chat messages and e-mails, but also that the person is of course working. You can expect a swift response.

2. Busy

This status usually gives the impression that someone is occupied with something important. If you want to reach this person, you could start with a chat message, to then switch to for instance a phone conversation or screen sharing. This is more effective than sending an e-mail. Only you cannot depend on a person to answer a chat message immediately. If the matter is urgent, you should call them.

3. In a meeting

A clear message: The person you would like to reach has an appointment and is therefore not able to answer the phone. Oftentimes a laptop is within reach/sight and you could ask a brief question via chat. Is it urgent and you are not getting a response? Send a WhatsApp or SMS. Can it ‘hold’ for a while? Set a ‘status alert’ meaning that you will receive a message as soon as that person is no longer in the meeting.
Note: Lync activates this status automatically if someone inserts a meeting or activity in his/her outlook calendar. If a meeting runs into overtime, the presence status will automatically switch back into ‘available’, unless it is amended manually.

4. Do not disturb

A person showing this status obviously does not want to be interrupted from his/her activities and responsibilities. The receiving of chat messages or phone calls whilst giving a presentation or working towards a deadline can be very disruptive, which is why Lync blocks these intrusions if you have activated this status. You can only inform this person via e-mail.
(Note: if you are giving the presentation it might be wise to ‘close’ your Outlook program, as the e-mail notification will briefly appear, and can distract you and your audience).

5. Be right back

Probably the most straightforward status to interpret correctly. Someone went to grab a cup of coffee or is consulting with a colleague. The status ‘busy’ or ‘do not disturb’ is not appropriate, as that implies that the person is in need of ‘some peace and quiet’ for an extended period of time. When a person consciously switches their status to ‘be right back’, that person expects people to hold off their attempts to get in touch. In this case it is useful to activate an alert status. Meaning that you do not have to continuously keep an eye on whether the person is available again, but will automatically receive notification.

6. Absent

This status can mean two things: The person has not touched his/her keypad for quite a while, which eventually causes the presence status to change to ‘absent’, or someone wants to indicate that he/she will not be behind their desk for some time. Often meaning that this person is ideally reachable via mobile phone or e-mail, in any case, sending a chat message will not have the desired response.