Explain the statement that oligopolistic markets such as supermarkets or car manufacturers can be defined in terms of market structure or market conduct.

An oligopoly is a type of market structure in which there are few firms with large market share and degree of monopoly power. Car manufacturers and supermarkets are an example of that.
Oligopolies are characterized by their structure or conduct. Here, there are few large firms that produce the entire output for that specific market, for example 4 firms with 25% market share each. There firms are interdependent (one firm's decision affects the decision of the other firms in the market) so the price and output of a firm will depend on how firms thinks the others will react. This can be explained using game theory, by illustrating the different decision structures that a firm can make and it actually makes. Market structure can also be defined in terms of the ease of entry and exit into the market. In an oligopoly, there are high barriers to entry, which prevent new firms from entering the market as a result of being tempted by the abnormal profits that they could potentially make. There can be natural, such as geographical, or artificial, such as advertising and branding, barriers.
The conduct of a firm represents its behavior within a market. Oligopolists do not compete over the price as prices are sticky. However, they compete on non-price basis such as product differentiation and customer service. For example Tesco has membership cards that earn customers points every time they purchase something. This is an incentive for brand loyalty and therefore, even if products of other companies are virtually the same, loyal customers will repeatedly repurchase the product no matter what the price is. Market price leadership is also a characteristic of the conduct of oligopolists, as it means that an oligopoly might be dominated by a firm at a point in time with others following it. After a while, firms take turns to be leader.
Therefore, an oligopoly is defined by its physical structure as well as its behavior in the market during its normal trading activities.