You've seen how 鉄 often has to do with railroad tracks, and this word is no exception — a private iron is a private railway.

In Japan, 私鉄 is the word for privately operated railway companies that were never part of the national Japan Railways system. Think of the big, non-JR commuter railways like Tokyu and Odakyu in Tokyo, or Hankyu in Kansai.

This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.