Infrared and Ultraviolet Divergences are two common words that you can find in every field theory calculation. Withholding their appearance, they are pretty much important for understanding a universe in the way we can. 

And there is a typical advancement of a particular theory with some hidden divergence, either infra or ultra. We believe that Infra means "under", so infrared typically means under some threshold. In contrast, ultra means higher. You can think of ultra as more complicated than infra, but both are pretty much abstruse topics.

There is a famous term which is, in fact, a whole subject called Renormalization. They forge the story of Renormalization between two likely descriptions, namely SFT and QFT. QFT had its pioneers, Gell-Mann and Francis Low, who constantly tried to overcome the divergences coming on a high energy scale in Feynman diagram scatterings. The simple, yet very un-intuitive, idea was to make the infinity absorbed in a certain quantity. However, this description had many flaws. However, it wasn't actually solved until Kenneth Wilson jumped to the subject with his Renormalization notion, which was completely out of the herd. He had his papers published in Physical Review and more writing length on the topic, which many wanted to ignore.

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And here we stop. There will be some series of blogs and writings on Renormalization, so more to follow up.