Try to delete entire row from table using delete button in PHP

To illustrate the comment above - the function does not know what the variable $id is as it is not defined within the function. So you can either assign as a parameter. Additionally, which I didn't immediately spot, was that the delete function similarly requires the $conn variable to be defined either as a parameter or as a global within the function itself.

The generated HTML was incorrect - the closing table row tag NEEDS to be within the loop and the th sections should be within a table row.

function delete($conn,$id){
    $delete1 =("DELETE FROM `usrdata` WHERE id = '$id'");
    $result = mysqli_query($conn,$delete1) or die(mysqli_error());
    echo "record deleted";
}

or declare as global within the function

function delete(){
    global $id;
    global $conn;
    $delete1 =("DELETE FROM `usrdata` WHERE id = '$id'");
    $result = mysqli_query($conn,$delete1) or die(mysqli_error());
    echo "record deleted";
}

The variable needs to be defined first, a hidden field in the form with the ID or some other means to define the variable.

Better yet would be to use a prepared statement in conjunction with the above so

function delete( $conn=false, $id=false ){
    if( $conn && $id ){
        $sql='delete from `usrdata` where id = ?';
        $stmt=$conn->prepare( $sql );
        if( $stmt ){
            $stmt->bind_param('i',$id);
            $result=$stmt->execute();
            $stmt->close();
            echo $result ? 'record deleted' : 'error';
        }
    }
}

As a possible solution, hastily written so excuse errors, you could perhaps do something like this:

The table is wholly contained within a form ( delrecord ) with a single hidden field id which is assigned a value by some javascript using the buttons dataset attribute data-id

<?php

    include 'conn.php';
    $result = ("SELECT * FROM usrdata"); 
    $count=mysqli_query( $conn, $result );


    if( $_SERVER['REQUEST_METHOD']=='POST' && !empty( $_POST['id'] ) ){

        function delete( $conn=false, $id=false ){
            if( $conn && $id ){
                $sql='delete from `usrdata` where id = ?';
                $stmt=$conn->prepare( $sql );
                if( $stmt ){
                    $stmt->bind_param('i',$id);
                    $result=$stmt->execute();
                    $stmt->close();
                    echo $result ? 'record deleted' : 'error';
                }
            }
        }

        $id=filter_input( INPUT_POST, 'id', FILTER_SANITIZE_NUMBER_INT );
        call_user_func( 'delete', $conn, $id );
    }


    echo'
    <form name=\'delrecord\' method=\'post\'>

        <input type=\'hidden\' id=\'h_id\' name=\'id\' />

        <table border=1px>
            <tr>
                <th>id</th>
                <th>email</th>
                <th>Password</th>
                <th>&nbsp;</th>
            </tr>';

    while( $data = mysqli_fetch_array( $count ) ) {
        echo"
            <tr>
                <td>{$data['id']}</td>
                <td>{$data['email']}</td>
                <td>{$data['password']}</td>
                <td><input data-id='{$data['id']}' type='button' name='delete' value='delete'></td>
            </tr>";
    }

    echo '
        </table>
    </form>

    <script>
        var col=Array.prototype.slice.call( document.querySelectorAll("input[type=\'button\'][name=\'delete\']") );
            col.forEach(function(bttn){
                bttn.onclick=function(event){
                    document.getElementById("h_id").value=this.dataset.id;
                    document.forms.delrecord.submit();
                }.bind(bttn)
            })
    </script>';
?>