WordPress "->" ?

What does “->” in wordpress stand for, I often see this being used in the wordpress loop, if statements and other places

I don’t see there is a documentation for this symbol in wordpress but is often used with other example….

Following are few “->” I have encountered so far:
/////////////////////////////////////

example 1:

$recentPosts = new WP_Query();
$recentPosts -> query('showposts=5');

//////////////////////////////////////

example 2:

while($selectedPosts -> have_posts()): $selectedPosts -> the_posts():
is used instead of
while(have_posts()): the_posts():

//////////////////////////////////////

example 3:

if($post -> post_parent){
   //??
}

//////////////////////////////////////

example 4:

$image = get_post_meta($post -> ID,'header_image', true);

//////////////////////////////////////

Can anyone explain the meaning of this symbol?