Illegal dismissal means an employee is being unfairly fired from their job. For example, if you went on holidays and the company hires a temp to fill in your position whilst you are on annual leave, when you come back from holidays, the job should still be there waiting for you. If your company lets the temp keep the job and gives you a position which now has lesser responsibilities and duties, and you resign, then the business has broken critical employment law and the business will be fined....Also, if you are pregnant and go on unpaid materiality leave, the business has to keep your job available for when you return. If they decide to fire you, then you have grounds to submit an unfair (or illegal) dismissal.......Also, a company cannot legally terminate your employment if you are not performing your job sufficient, if you do not receive a first, second written warning. For example, if your job performance is average, they cannot sack you until they have given you an advance warning to improve, and the business must have written plans on how to help you improve. If you are still not performing, they will then give you a second notice, if you continue to fail, then they can sack you.
Also in some countries like overhere it is illegal to dismiss someone without giving them a proper warning before. Basically anything that is in contravention with any law or regulation when dismissing someone, like jaz pointed out it can also be because of race, religion etc.
i would think its a boss firing you from work for a reason thats is not legal...like because of your race, colour, religion, gender, ect.