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Help understanding properties with underscores.

I'm following a few tutorials on implementing frameworks and in the implementation file I'm seeing the properties written with underscores. Code is in Objective C.

For example

I'm working with the Multipeer Connectivity Framework and the properties are

@property (nonatomic,strong) MCPeerID *peerID; @property (nonatomic,strong) MCSession *session; @property (nonatomic,strong) MCBrowserViewController *browser; @property (nonatomic,strong) MCAdvertiserAssistant *advertiser;

And the initializer is written like this:

-(id)init{ self = [super init];

if (self) {
    _peerID = nil;
    _session = nil;
    _browser = nil;
    _advertiser = nil;

return self;


Are _peerID, _session, _browser and _advertiser referring to "this" particular item in the object ?