The most usual meaning of this term refers to an approach in which firms' marketing strategy is driven by environmental factors. This does not refer to environmentalism but rather to the "environment" both within the firm and in the market in which the firm is trying to sell its product.
When marketing its products, a firm must consider its external environment. It must, for example, consider the culture of the marrket in which it is selling. This might mean that an ad campaign in the United States can make much more use of sexual imagery than an ad campaign in a more culturally conservative market.
A firm must also consider its internal environment. This can include such things as the overall financial health of the company. A company with greater cash flow, for example, can choose more expensive kinds of marketing.
Overall, then, an environmental approach to marketing is one that takes into account a firm's internal and external environment.