The term "single cell" refers to an individual cell, isolated and examined on its own. Analysis conducted specifically on individual cells is collectively referred to as single-cell sequencing analysis, while sequencing performed on these isolated cells is termed single-cell sequencing. Sequencing multiple cells or a group of cells falls outside the realm of single-cell sequencing. For instance, common genetic sequencing practices, often performed for public interest, entail extracting specific DNA fragments after minimal blood processing. However, it remains uncertain whether the extracted DNA originates from a particular white blood cell, another white blood cell, or free DNA circulating in the bloodstream. Similarly, in conventional tumor studies, sequencing is typically conducted on numerous tumor cells isolated from tumor tissue. [Single-cell sequencing for oncology](https://singlecell.creative-biolabs.com/single-cell-omics-solutions-for-oncology.htm) represents a specialized form of sequencing; currently, the majority of sequencing efforts do not operate at the single-cell level. To grasp the technical aspects of single-cell sequencing and analyze its advantages, it's crucial to understand the precise meanings of terms such as "single-cell sequencing" and "high-throughput technology." We need to discern what these terms entail when prefixed with "single cell" or "high-throughput." The fundamental significance of single-cell sequencing lies in cellular heterogeneity. This implies that individual cells exhibit variability, even among cells from the same location, potentially resulting in differences in gene expression and other attributes. Studying cell populations only provides averaged outcomes, masking cellular heterogeneity. Two specific examples illustrate this: Firstly, cell classification. Historically, cell classification relied on characteristics like spatial position and morphology, which is a relatively crude method. Conducting [single-cell RNA or DNA sequencing](https://singlecell.creative-biolabs.com/single-cell-sequencing-analysis.htm) enables a more nuanced and rigorous cell classification, particularly beneficial for complex tissues, facilitating a deeper understanding of cellular functions. Secondly, studies related to tumors. A widely accepted hypothesis regarding tumor metastasis posits that certain cells from a tumor may detach, enter the bloodstream, and become circulating tumor cells ([CTCs](https://singlecell.creative-biolabs.com/single-cell-omics-solutions-for-circulating-tumor-cells.htm)). Some CTCs may travel to an organ via the bloodstream, invade blood vessels, infiltrate the organ, adhere, proliferate, and form new tumors. Determining which cells from the original tumor become CTCs, which CTCs can survive in the bloodstream, and complete tumor metastasis requires single-cell level sequencing and other related research endeavors. In conclusion, the advent of single-cell sequencing has opened new vistas in our understanding of cellular biology, particularly in unraveling the complexities of cellular heterogeneity. By delving into the intricacies of individual cells, we can uncover insights that were previously obscured by population-level analyses. This approach holds immense promise in various fields, from advancing our knowledge of basic cellular functions to revolutionizing our understanding of diseases like cancer. As we continue to refine and expand single-cell sequencing technologies, we can anticipate even greater breakthroughs on the horizon, unlocking the full potential of this powerful tool in biological research and clinical practice.