Synthetic data has become a crucial tool in training large foundation models, particularly when real-world data is scarce, sensitive, or costly to collect. This artificially generated data is used to expand datasets in various domains, such as medical imaging, financial tabular data, and software code, while also addressing privacy concerns. Different techniques are applied based on the domain, including Bayesian networks, GANs, diffusion models, and large language models (LLMs), each with its strengths and limitations. In medical imaging, synthetic data helps to overcome the scarcity of high-quality, labeled scans while protecting patient privacy. In finance, it enables analysis while complying with strict privacy regulations, and in software, it aids in training and testing code generation models. However, synthetic data is not a perfect substitute for real data, as its effectiveness hinges on its ability to accurately replicate real-world patterns and complexities. The ongoing development of these techniques continues to enhance the robustness and scalability of foundation models, although challenges such as high computational demands and the need for domain-specific adaptations remain.