A forced marriage is where one or both parties are coerced into marrying someone against their will. They may be physically threatened or emotionally blackmailed to do so. It is an abuse of human rights and cannot be justified on any religious or cultural basis. It's not the same as an arranged marriage where you have a choice as to whether to accept the arrangement or not.
There is now legislation in place in Scotland to protect victims or potential victims of forced marriage.
• The Forced Marriage Unit, a joint initiative with the Home Office currently sees over 1600 reports of forced marriage a year.
A 'so called honour killing' is the murder of a woman accused of bringing shame upon her family. Some of the most common reasons for murdering a family member include: refusal to enter an arranged marriage, seeking a divorce - including from an abusive husband - or committing adultery. In some cases, women who have been sexually assaulted or raped are then murdered for the "dishonour" of having been a victim of an attack. Police believe there may be as many as 12 honour killings in the UK each year.
http://www.bbc.co.uk/ethics/honourcrimes/crimesofhonour_2.shtml