Concept:
A gland is an organ that secretes substances required for body functions.
Step 1: Understanding liver.
The liver is a large organ present in the upper right part of the abdomen.
Step 2: Glandular function.
The liver secretes bile, which helps in digestion and absorption of fats.
Step 3: Largest gland.
The liver is the largest gland in the human body.
Step 4: Checking other options.
Pituitary is called the master endocrine gland but is very small.
Thyroid is an endocrine gland but not the largest gland.
Pancreas is a mixed gland but smaller than liver.
Therefore, liver is correct.
\[
\boxed{\text{Liver}}
\]