A falsecard is a card that is played in attempt to deceive one or more players at the table. Falsecards are not unethical. You can falsecard as much as you want, although prudence is invariably the golden rule for success. There are random falsecards novices make which sometimes help the opposition, and there are intelligent falsecards good players make that have a reasonable chance of succeeding. When in doubt, it's better to not falsecard at all. At least that way partner will never be misled into the losing action. Like a bad psych, a bad falsecard will upset him to no end.

The only type of falsecarding that is banned is purposeful falsecarding that a partnership has agreed to use in certain situations. For example, against notrump contracts, a player often leads the fourth-highest card of her longest suit. If she decides to make her opening lead from a suit such as A9753, and she and her partner have agreed to use fourth-highest leads, she would normally lead the 5. What she cannot do is tell her opponents that her side has agreed to fourth-highest leads, but then continually lead, say, her third-highest card. Obviously her partner is going to know what's going on after a while, whereas various declarers will always think her lead is fourth-best. This type of falsecarding is unethical.