Lakshman Rekha, in Hindu mythology, is a line drawn by Lakshmana around their abode, to protect Sita, while he is away searching for Rama. As explained in the epic Ramayana, Rama goes chasing a deer,which is actually the demon Maricha in disguise, and does not return for long. Lakshmana who cannot bear to see Sita cry in grief, decides to go and search for Rama, subject to his condition that Sita should not cross the line he draws, so that she would be protected in his absence. Anybody attempting to harm Sita across the line would be singed by flames erupting from the line.
Once Lakshmana leaves in search of Rama, the Rakshasa king Ravana comes in the form of a sage and asks Sita for alms. Not expecting a trick, she unsuspectingly crosses the Lakshman Rekha to provide alms to him and Ravana kidnaps her in his Pushpaka Vimana.
Lakshman Rekha, in modern Indian parlance, refers to a strict convention or a rule, never to be broken. It often refers to the ethical limits of an action, traversing which may lead to undesirable consequences.
