A termination letter is a letter from an employer to an employee informing the employee of the termination of their employment. This particular letter is written for those instances where the employer is terminating the employee "for cause" (e.g. the employee's work was deficient in some way - chronic tardiness, poor work quality, etc.).
You must be aware that you must use proper dismissal procedures to ensure that you are fair, consistent, and legally proper. Employment law must be followed, otherwise you and your company is at real risk of disputes from disgruntled ex-employees and ensuing penalties. In all cases, refer to your local expert on employment law to ensure you are compliant and compassionate.