What is the meaning of Metasyntactic_variable?

5-letter words containing

• 5-letter words containing d

• 5-letter words containing e

• 5-letter words containing o

• 5-letter words containing c

• 5-letter words containing t

5-letter words starting with

• 5-letter words starting with r

• 5-letter words starting with z

• 5-letter words starting with m

• 5-letter words starting with u

• 5-letter words starting with u

5-letter words in the middle

• 5-letter words in the middle n

• 5-letter words in the middle s

• 5-letter words in the middle i

• 5-letter words in the middle a

• 5-letter words in the middle a

5-letter words ending with

• 5-letter words ending with l

• 5-letter words ending with n

• 5-letter words ending with m

• 5-letter words ending with r

• 5-letter words ending with e

5-letter words excluding

• 5-letter words excluding i

• 5-letter words excluding d

• 5-letter words excluding t

• 5-letter words excluding c

• 5-letter words excluding s