In my limited understanding, it is a spirit number or angel number. I get a variety of repeating numbers from my spirit guides.
There's a lot of interpretations around the internet. Usually (though not always) most sites say similar things. The site that I usually refer to is this one:
http://www.spiritual-path.com/numerology.htm
According to that site, repeating 333s or 3333s means:
"This sign indicates that your Spirit Guides agree with your thoughts and feelings and could be interpreted as a Cosmic 'Yes!' to questions you have asked or ideas you may have."
Another good site is:
http://spiritlibrary.com/doreen-virt...rom-the-angels I guess that may be the one you are referring to, as this site says (for 333s and 3333s):
"The Ascended Masters are near you, desiring you to know that you have their help, love, and companionship. Call upon the Ascended Masters often, especially when you see the number 3 patterns around you. Some of the more famous Ascended Masters include: Jesus, Moses, Mary, Quan Yin, and Yogananda."
So...take your pick I guess. Which one seems to resonate for you?