especially vs that is

especially

adv
  • Used to place greater emphasis upon someone or something. 

  • In a special manner; specially. 

  • Particularly; to a greater extent than is normal. 

that is

adv
  • In other words; that is to say. Used to introduce a clarification or explanation 

How often have the words especially and that is occurred in a corpus of books? (source: Google Ngram Viewer )