What is an informal interview?

If you were invited to a Informal Interview, you would be wise to prepare for and address it as you would any other type of interview, do not think of it as anything other than an interview.
If you are looking to set it up yourself, here is some tips I would like to share.
Informational / Informal Interview
This is unlike all of the other types of interviews. In an informational interview you, the job seeker will initiate and set up the interview with someone within the corporation or industry that you are pursuing a position. This falls under the umbrella of networking and it really requires much the same skills as a sales person making a cold call. Even astute job seekers tend to leave this type of interview out of their job seeking regiment because they are either not aware of the process or it may seem daunting.
For that reason, including this strategy into your job search process will give you an advantage over applicants that do not use this procedure. Seeking a dream job is a full time job and as with any job, the people that go the extra mile are more likely to be successful.  In this type interview, the job seeker has much more control of the process and it is far less stressful because you are not seeking placement at this time only information. Therefore, it is also easier on the person you are interviewing due to the facts; 1) they will be flattered you are asking for their opinion and suggestions 2) they do not have to make a hiring decision on you when the interview is over.
You must be well organized and prepared to get all you can out of this opportunity. You still will need to do all of the preparation and research as you would for any other interview so you can prepare a list of the key questions you want to ask before you set up this meeting.
Two suggestions on how to set this type of interview up are, you can visit a location of the company and seek out a contact or you may place a call to the location and try to make a connection with a contact that you may meet with later. It is not a good idea to hold the interview itself by phone because your contact will most likely be more reluctant to speak openly with someone he or she cannot see or may become uneasy at some point of your questioning. 
The purpose of this type of interview is to:
Network
Get answers to a comprehensive list of questions you prepared before hand
Seek advice and insight from people in the job you are seeking
Get to know people in the industry or company
Get leads on possible openings
Get to know who may make the hiring decision
Get the names of possible contacts for later
Find out what the company’s expectations and priorities are
Build a relationship with this person so they may refer you