what is the benifit of using woff font file

Question

I saw example of a site which is using a separate font file (woff) and using the source code as

<span id="txt44_1109014" data-width="147.274994" style="left:
58.538px; top: 23.413px; letter-spacing: -0.596739391304348px;">®euee&nbsp;Deelee&nbsp;DeeHeCe&nbsp;³ee</span>

Below are the CSS for this element

#txt44_1109014, #txt45_1109014, #txt46_1109014 {
  font-family: fnt0;
  font-size: 25px;
  line-height: 29px;
  font-weight: bold;
  color: #000000;
}

In the source code I saw there is a .woff font file which is coming from network(server). I want to know what is this method(any specific name)? We can do same thing via usign unicodes still what is the benific of this? Any standard document for this present on net?