What is the difference between idioms and similes

journalism is the gathering, organizing, and distribution of news -- to include feature stories and commentary -- through the wide variety of print and non-print media outlets. it is not a recent phenomenon, by any means; the earliest reference to a journalistic product comes from rome circa 59 b.c., when news was recorded in a circular called the acta diurna. it enjoyed daily publication and was hung strategically throughout the city for all to read, or for those who were able to read.

i’m not sure but i believe it is true