Difference between slf4j-log4j12 vs log4j

[Debraj Manna]

Crossposting from stackoverflow
<https://stackoverflow.com/questions/47574644/difference-between-slf4j-log4j12-vs-log4j>

In a project's pom.xml I am seeing a dependency like below

<dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.5</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.7.5</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>


Can someone let me know what is the difference between slf-log4j12 & log4j ?