The term Top Line refers to a company's gross revenue or total sales. It is called the "top line" because it appears at the top of a company's income statement. The top line reflects the total income from all sources, primarily from sales of products and services, before subtracting any costs or expenses. 
The top line is a crucial indicator of a company's business volume and the initial measure of its operational efficiency. It gives an overview of the scale of a company's market operations. However, it does not account for the cost of goods sold (COGS), operating expenses, or other costs, which are subtracted to calculate the net income or "bottom line."
The importance of the top line varies across industries and companies. For example, in a high growth industry, a strong top line growth can indicate market acceptance and scaling opportunities. However, it's also important to note that high top line growth isn't always synonymous with profitability. If production, operation, and sales costs are high, a company might have a large top line but still not be profitable.
In terms of management, companies can try to boost their top line by increasing sales volumes, raising prices, expanding their market, or introducing new products. However, the key to sustainable business success lies in maintaining a balance between increasing the top line and managing costs to ensure a healthy bottom line.
The top line is often used to compare companies within the same industry and can be used to measure growth by comparing the top line figures over different financial periods. Over time, a consistently increasing top line often signals good performance, assuming costs are well-managed.
To illustrate, if a car manufacturing company had total revenues of $20 million in a year solely from its sales, this amount would represent the company's top line. However, this does not take into account the costs of production, operating expenses, interest payments, taxes, and other costs that will be subtracted to yield the net income or "bottom line."
- Definition - What Does Top Line Mean? Investopedia