That is "eggwhite cervical mucus."
The cervix (which is the opening from the vagina into the uterus, at the bottom of the uterus) produces different kinds of secretions and mucus at different times of your menstrual month that do different things.
Eggwhite cervical mucus is slippery, stretchy and clear, and if you look at it through a microscope, its cells tend to align (like straight hair) instead of knit together (like wool). This is to help sperm travel up into your uterus and Fallopian tubes. It happens about 2-4 days or in your month, just before you ovulate and probably when you ovulate also.
The other kind of secretions you will see are more cloudy, more watery or milky, and they dry yellowish-green in your underwear. Those are vaginal secretions and mucus for non-ovulating times of the month. Under a microscope they look more designed to block sperm (or at least not to glide it along) and they are also there to clean the vagina.
The description of EWCM is that you could almost snip it with scissors, and it's clear enough to read a newspaper through. You could hardly have painted a more accurate picture of what it is. Sorry it alarmed you!
What it means is that ovulation is going to happen in the next 1-4 days or so.
You could chart your EWCM days and your period days on graph paper, starting a new line whenever a new period comes, and over a few months it will give you a pretty clear picture of when the expect your period and ovulation.
Yes, I agree. Our discharge will change consistency and even color based on hormones. At around the time of ovulation, it can be clear and kind of gooey or stingy. It's perfectly normal. Only really worry about discharge if it smells bad or you itch.