I have a lump at the back left side of my neck, what does this mean?

Many. It could be one of many things. No point anyone guessing online. Please get examined by a doctor. Good luck.
Depends. This could be cyst, mole or any lymph nodes. Please see a doctor to get it checked.
Many things. Palpatory lumps at the neck can be due to enlarged lymph nodes, thyroid nodules, lipoma, abscess, and other etiologies. Painless, nonmobile enlargement of the lymph nodes as a warning sign of underlying occult malignancy. Examination and evaluation by a physician is recommended to ruled out serious underlying conditions (e.g. lymphoma, neoplasm).