Throughout equalities related guidance from the Equality & Human RIghts Commission you will see reference to 'protected characteristics' (as detailed in the Equality Act 2010). This page gives you more information on each of the nine protected characteristics.
Where this is referred to, it refers to a person belonging to a particular age (e.g. 32 year olds) or range of ages (e.g. 18 - 30 year olds).
A person has a disability if s/he has a physical or mental impairment which has a substantial and long-term adverse effect on that person's ability to carry out normal day-to-day activities.
The process of transitioning from one gender to another.
Marriage and civil partnership
In England and Wales marriage is no longer restricted to a union between a man and a woman but now includes a marriage between a same-sex couple.  This will also be true in Scotland when the relevant legislation is brought into force. 
Same-sex couples can also have their relationships legally recognised as 'civil partnerships'. Civil partners must not be treated less favourably than married couples (except where permitted by the Equality Act).
Pregnancy and maternity
Pregnancy is the condition of being pregnant or expecting a baby. Maternity refers to the period after the birth, and is linked to maternity leave in the employment context. In the non-work context, protection against maternity discrimination is for 26 weeks after giving birth, and this includes treating a woman unfavourably because she is breastfeeding.
Refers to the protected characteristic of Race. It refers to a group of people defined by their race, colour, and nationality (including citizenship) ethnic or national origins.
Religion and belief
Religion has the meaning usually given to it but belief includes religious and philosophical beliefs including lack of belief (e.g. Atheism). Generally, a belief should affect your life choices or the way you live for it to be included in the definition.
A man or a woman.
Whether a person's sexual attraction is towards their own sex, the opposite sex or to both sexes.
 Section 1, Marriage (Same Sex Couples) Act 2013.
 Marriage and Civil Partnership (Scotland) Act 2014.