An escape fund is traditionally a secret bank account an abused wife opens. As the name implies, it is meant to be a secret cache of money the wife will one day use to escape from her husband when the figure grows to some predetermined figure. Escape funds are traditionally opened by a wife who doesn't work and is probably not allowed to work by a domineering husband. The accumulation of money in the escape fund is done usually by skimming money from whatever stipend the husband gives the wife to manage the household finances or to buy groceries and cleaning products.

(And while I joke about it a bit here, an acquaintance was just relating to me today about a friend of hers who was taught from childhood by her mom that creating an escape fund was a normal part of a woman's management of household finances. Scary, no.)

Escape fund might also be used somewhat sarcastically by people who work abroad or possibly work in country but far away from family and friends. It's money ear marked in case one needs to do a "midnight run", that is move on very short notice.

As Master Villain pointed out to me, many times people living with their parents might accumulate an escape fund. The term might be used sarcastically in the cases where parents provide a benign, cushy, hard-to-leave home life and you're just itching to live on your own. Or it might be used in an all-too-real sense where you're living with insane, controlling, mercurial parents.