The English word mammon originated from a Greek word, which itself originated from a Babylonian word, that referred to personified wealth. In the New Testament era, mammon was the name of a Syrian idol that represented worldly riches i.e. the term is used in Christian teaching to describe making an idol out of the acquisition or possession of worldly wealth. Perhaps a modern-day example of the same thing is how some people idolatrously (whether they realize that they are doing it or not) use the term "the almighty dollar" - "The Almighty" is a designation that belongs to God alone.
"Ye cannot serve God and mammon"
While Christians recognize the necessity to work to make a living (the Fourth Commandment commands to rest on the Seventh Day and to work on the other six days of the week), they do not put the pursuit of money ahead of their obedience to God. The parable of the shrewd manager was also about salvaging ("salvation" is from the same root; see also Sealed Unto The Day Of Redemption and Why Does God Allow Evil?) value from what could otherwise be lost. Christ was not commending the conniving methods of the steward; He was saying "16:13 No servant can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon" (Luke 16:13 KJV).
"16:1 And he said also unto his disciples, There was a certain rich man, which had a steward; and the same was accused unto him that he had wasted his goods. 16:2 And he called him, and said unto him, How is it that I hear this of thee? give an account of thy stewardship; for thou mayest be no longer steward.
Fact Finder: What sort of "mansion" did Christ promise His people?