## 2 Background, Definitions and Motivation  
### Online Reviews  
A review can be defined as feedback of specific products from specific users to inform particular individuals. [PERSON] et al. (2015) described online reviews as Electronic word-of-mouth (eWOM). The eWOM is informal communications about usage or features of goods, services, or their sellers geared towards consumers through an internet-based technology. On the other hand, [PERSON]. (2016) stated that reviews are popular user-generated content (UGC) that consumers utilize when doing different decisions related to travel, buying, renting, and using a service. Reading such reviews can reduce risk, make new ideas, streamline choices and emphasize choices for consumers. While the work in (2016), interprets online reviews as a process that previous consumers provide to criticize products. That being said, reviews are known as an information source for marketers and consumers in order to learn product quality. Also, reviews are considered a useful metric  
Figure 1: Type of approaches to detect spam reviews used in this study. to measure the loyalty of consumers in situations like product's success critical implications [54]. Therefore, providing reviews can benefit many related parties to study the products in different aspects to confirm the quality, sales, reputation, and market share of the product. Others consider reviews more credible and essential than the data presented by the commercial sources [55]. Moreover, reviews could affect several facets of products such as revenue, prices, performance, and popularity. According to European Consumer Centres, there are more than 80% of consumers read reviews before purchasing [56]. Online reviews have a primary and critical impact on e-commerce, particularly, shopping decisions and the amount of money that could be spent. For that reason, reviews are known as one of the important aspects of business performance [57]. Reviews usually has a heavy effect on consumers buying behavior in various product categories, including, games [58], movies [59], restaurants [60], and books [61]. [PERSON] et al. [51] states that alongside reviews, also rating could impact consumers' attitudes. A number of studies take into account the rating as an element of reviews that also have some kind of effect on consumers [62; 63]. Therefore, [PERSON]. [59] demonstrates that consumers now have access to any information and exchange opinions on products, services, and companies easily. As a result, more businesses begin to offer online services for consumers to write their reviews. Examples of such services are Amazon, Yelp, IMDb, Metacritic, and so on. Further, ABC, CBS, and NBC television networks provided a place for viewers to discuss their shows and programs online [59]. Hence, making the web more like a medium to reach people in order to generate more awareness of their products and services. Also, with the different types of reviewers' argument quality, readers could easily differentiate with certain reviews. Thus, many websites offer the ability for readers to rate reviews to be useful or not for them [64]. All these features made reviews more crucial every day. Especially at this time when all countries suffer from the pandemic and forcing people to stay in their homes, which made the dependence on online reviews higher than ever. In summary, online reviews become more needed than ever due to different aspects, such as knowing the quality of the products, making the right decisions about what to buy. Moreover, feedback for companies, manufacturers, and owners, as well as staying at homes due to the COVID-19 pandemic situation (quarantine). These aspects or reasons increased the importance and popularity of online reviews. Therefore, the number of platforms that support online reviews increased. However, due to the widespread and simplicity of users who post and read reviews, it becomes more exposed to turn these reviews into negative opinions, namely, spam reviews.