At the open stage, the lead has shown some sort of interest in the product. No personal involvement has happened at this point, but the lead may have gone to your website or viewed an ad for your product that was aimed at them.
The next stage of a lead involves having made personal contact with them. This can be through an e-mail, a phone call, a meeting, etc. Using data collected about open leads can help determine which leads to connect with first.
Throughout contact with a lead, the end ideal stage is a sales ready opportunity. This is the stage at which the lead is ready to be passed to the sales. A qualified lead should have a budget and the decision making power to make a purchase from your company.