Explain Eloquent relationships with code examples.

class User extends Model {
    public function profile() {
        return $this->hasOne(Profile::class);
    }
}

class Profile extends Model {
    public function user() {
        return $this->belongsTo(User::class);
    }
}

class Post extends Model {
    public function comments() {
        return $this->hasMany(Comment::class);
    }
}

class Comment extends Model {
    public function post() {
        return $this->belongsTo(Post::class);
    }
}

class User extends Model {
    public function roles() {
        return $this->belongsToMany(Role::class);
    }
}