Oedema refers to the swelling or accumulation of fluid in the body's tissues. It can occur due to various reasons such as injury, inflammation, heart failure, kidney disease, or liver disease. The buildup of fluid causes an increase in blood volume and leads to symptoms like swollen limbs, face or abdomen, difficulty breathing, and weight gain. Oedema can be classified into two types: pitting oedema (where a indentation remains after pressure is applied) and non-pitting oedema (where an indentation does not remain).