This card is a dark omen. Like the rest of its suit, it is bound your emotions, and it brings with it a warning of loss and disappointment. Expect a setback in your life, almost certainly emotional. It may be a project or goal you are particularly invested in emotionally. In certain positions it might also refer to events of the past which continue to cause regret or heartache. The only solution is optimism; this too shall pass.
To get the full traditional meaning and interpreation of Five Of Cups, I suggest you visit Trusted Tarot and their Five Of Cups page.